Because you make a build and stick with it, unless its in your characters 'arc' to change in someway. Sounds to me like people just want to make JOAT characters that do everything in the game, which is basically just playing it like an action game. People always talke about choices making an RPG, well our choosing what ind of build your making. A birth sign was some huge game breaking feature? No, neither was picking specialties, majors etc.
You don't seem to understand this "be who you play" thing Bethesda does...
You create your character DURING THE GAME, not at the beginning. You make choices every level up and even beyond.
There are still limitations, the 50 perks for one, so you cannot do everything with one character.
If you dont like your build, or your getting tired of it, make another.
Ah yes... I'm in the middle of the game, only to realise my current build svcks.
Oh welll, I can start over, losing all the progress and achievement I've made, only to do it again, maybe next time it will be different...
FUN!