Target lock gets disabled because its honestly more of a hindrance than a help.

Especially in a lot of more recent content where mechanics and stuff happen outside the arena so are invisible if your looking at the boss. Combine that with bosses getting bigger and bigger if you use target lock they can easily take up 3/4 of your screen..

The camera does need some changes doing good it though that's a fairly common comment even just being able to zoom out further would be a massive help to many players. As at least then you could keep yourself and the boss on screen and still have a decent view of what's going on around you.