I think you meant it the other way around - "why custom ROMs have little device support" - right?

because for me it's clear that companies just want to ship their own spyware and bloatware.

In many cases, because manufacturers refuse to allow unlocking of bootloaders. In other cases, because manufacturers refuse to share drivers for proprietary hardware.

It just feels like I don't need custom ROMs anymore. Nowadays, most phones already do what I want them to do. I used to be pretty deep in the custom ROM community, but nowadays I don't even think about rooting my phone.

I guess the only use case for custom ROMs is the privacy aspect. But most people don't care about it, so the support is abysmal.

I am presently using a super niche device. SUPER niche. So niche that I have been dealing really closely with the manufacturer, who worked with Qualcomm and made a specific firmware just to get wifi calling working for me in Australia.

I have quizzed them so many times on why they won't support rom development. You can unlock the bootloader, but the rom files are heavily encrypted. There's no way to extract the boot IMG so we're dead in our tracks.

The manufacturer basically say that they have to fight so hard to gain google certification that they won't do a single thing to risk losing it.

They've been pretty generous with their warranty policies so probably another reason is they don't want to risk anyone doing overclocking etc and then having to cover device repairs or replacement.

I used to install custom roms all the time back before knox on Samsung, now I cannot be bothered, usually something in the roms does not work among other bugs, it takes too long to keep up to date on rooting stuff etc, the support for roms is abysmal. I started to lose interest around the time banking apps started detecting root and not working, there were ways around it with magisk but it was complicated and could not find decent documentation on it.

It just became simpler to use what's out of the box and the newer phones I started buying had very little in the way of custom roms to start with.

It's mostly a function of an unlockable bootloader. If the device manufacturer does not allow the bootloader to get unlocked then putting a ROM on it is extremely difficult.

Pixel devices tend to be unlocked, unless the carrier locks the bootloader. So it's always a good idea to buy pixel directly from Google so you get an unlocked bootloader.

The same can be said for fair phone.

The other devices are really hit and miss. Basically if you can't control the software it's not your hardware even if you paid for it.

Fairphone, they have instructions even on their site on how to flag your phone with different OS's. Think it's just been released in the states too. Android AOSP, Lineage, Ubuntu Touch, eOS to name a few.

Xiaomi phones with Snapdragon SoCs have very good custom ROM support.

I'm not sure that is true, I don't remember device support being much better in the past. But assuming that is the case, part of the reason might be the fast evolution of devices and Android itself back in the day. Old devices quickly becoming obsolete and new Android versions being desirable made custom ROMs very attractive for a group of people, including myself.

I installed CyanogenMod on my first smartphone because I could get a more recent Android version when it actually made a difference. As Android evolved, an up-to-date install is not as different anymore than a 3 year-old one, not in features and even less in looks. The main motivations I see for custom ROMs nowadays is to improve your privacy and decrease bloatware, but I don't think most users would bother with going through the process and voiding their warranty to have these things.

I think there are fewer people working on them, more complexity involved in making a good one, and fewer end-users who want to use them.

It's disappointing that every device needs active effort to support it, unlike PCs where operating systems can be more generic and detect hardware during boot or install. It's my understanding that newer Android versions have improved the situation some, so we may see things turn around a little.

Unlockable bootloaders, having adb and fastboot support on the phone side, having a processor that has open source code, and not disabling cameras etc when the bootloader is unlocked are all needed to have a viable custom ROM community for a specific device.

Lots of modern phones don't do some or all of the above. Mediatek powered phones are a no-go, some phones don't support adb or fastboot (iirc some older LG phones have this issue), Sony would disable the camera if a bootloader was unlocked on some of their older phones.

I have an android that has Mediatek Dimensity and I have found 0 custom roms that are good. I wonder why.

I understand your bad experience with GSIs, but I think it's a step in the right direction. The way custom roms have been made through the years isn't sustainable for the long run. It's too much work for the few people involved, that goes obsolete so fast. But with GSis, the projects will one day be able to maintain just a few images, and the porting community will just have to focus on unlocking the devices.

GSIs aren't working 100% today, but it's something still new in the perspective of manufacturers, and the tendency is to have better support with time.

Just to put things into perspective, my experience, as someone poor from a third word country, is just the opposite. In the past, only the more expensive phones had custom rom support, and the cheaper ones I got access to, wouldn't even get results if I searched for the model on xda. Nowadays, even cheap chinese phones or the ones locally manufactured in here allow me to put a GSI and have a customized experience, up to date with security patches.

For Samsung specifically, they flip a fuse if you unlock the bootloader which permanently disables many security features. That is a major issue for anyone wanting to do things responsibly.

There are still plenty of custom ROM communities out there, but mostly for those cheap Chinese brands, especially those with snapdragon SoC. Enthusiasts using those devices usually aren't too afraid of breaking their cheap phones, so the communities are still thriving. On the other hands, people with $1000+ flagship phones are usually less likely to do this and void their warranty, unless their phone manufacturers aren't voiding warranty when you unlock the bootloader such as on pixel devices.

I can't see many advantages to the manufacturers.

If people were screaming out for this I'm sure plenty of marketing departments would jump on it.

I also imagine as hardware gets more complicated so does the process of making ROMs. Which is already a pretty niche skill.

Most manufacturers have made it more difficult to both make and install custom ROMs for their devices.

Pixel is the one big exception so far.