You're mistakenly thinking people are buying vinyl records for sound quality, and there may be a few misguided people out there, but the vast majority aren't.

For many it's about simply supporting their favourite artists, and getting a cool item to enjoy. I'd say most vinyl record gatefolds often have a load of extra interesting stuff going on compared to a CD jewel case release. It also lends itself to forcing you to be more deliberate about listening, you need to pay attention to flip the record, you need to physically interact with the thing—I imagine the majority that still buy CDs end up just ripping them to another device and then basically never open the case again. Which I'd say encourages entirely different kinds of listening experience. Neither are invalid ways to engage with an album.

I guess that leads onto the other thing to point out, which is most of the modern records I buy come with a code to download FLACs of the album, sometimes even at higher quality (24-bit/96khz) than a CD release (16-bit/44.1khz). This is also more convenient for increasing numbers of people that simply don't have a way to play CDs at all any more, let alone on a hi-fi or something.

I'll agree though that most people are listening with mediocre equipment. But FWIW, there are fantastic quality "ear bud" style IEMs out there (I like Shure's range) that'll blow a lot of non-professional headphones out the water.