Working on LineageOS doesn't help you if you can't even install it. Fewer and fewer phones come with unlockable bootloaders these days. The grip is tightening.

right, but if you can't install a custom android, you can't install anything linux based or anything else for that matter. so that's a different issue entirely.

Yes, but if you are building your own phone hardware to run Linux on it, there is a huge advantage in that Linux flavor being an AOSP fork, since it is already mature.