Phone needs a big update? Download a bunch of movies and music?
Like, plug it in for 5 minutes to get gigabit speed and download 35gb of data.

Not an average use case, but I used to use iPads on a tradeshow floor demonstrating apps and controlling other smarthome devices on a network. Wi-Fi at tradeshows is abysmal at best, so we would connect the lighting to USB adapter, then connect a USB to ethernet dongle for hardwired network that was stable. Worked great for us.

i can think of lots of reasons, all of them niche or not for regular use.

but there are use-cases, and ios already has drivers for usb nics, so a better question might be “what good reason is there not to support this?”

Large network transactions (like an initial download when transferring phones) are a lot “kinder” to the hardware if you’re pulling through the port rather than running the wireless radios. There’s enough activity on the SOC already, can keep excess heat down by not needing the WiFi pumping at hundreds of MBs as well.

I could see people docking their phones, and having a keyboard, mouse, external monitor, ethernet, speakers, etc. connected to the dock. I do that with my steam deck to play games on the TV. Apple is pushing gaming hard with the iPhone 15. I could see that being a use case Apple would support for gaming.

It depends. I do it from time to time whenever my internet connection is faster than my mobile data or I want to avoid hitting my data limit needlessly when I have a cord already in the room.