Roms face a different problem: bootloader locking. But the more Android changes drastically, the harder it is to integrate the AOSP changes into the different open projects
Is that a problem these days? It was over a decade ago that I last needed to jailbreak a phone, nowadays it’s just "I’d like to unlock" "Ok".
Source: 7 years of running deGoogled Android phones and 11 years of running ROM’d Android phones before recently moving to iOS and giving up.
So not as great as I thought, but also not as bad as you made it seem ;)
[0]: https://github.com/zenfyrdev/bootloader-unlock-wall-of-shame...
Pretty sure I read Google was no longer going to publish device tree sources for Pixel phones, which will make ROM development for them significantly harder, whether or not the bootloader is open.