Fallout has turn-based combat because of X-COM. Tim Cain said so. I suspect combat was going to be more tactical, but things changed when they lost the GURPS License and had to improvise.
Tactics was nice, even CTB was nice, but its agreed that RT combat was a mistake and they should have focused on a deeper turn-based experience. Its also a very linear game and lacks environment destruction.
Fallout had turn-based combat...but it only has one controllable unit, so the meaningful benefits of turn-based combat were pretty much entirely lost. You picked your one move you had built into your character and you spammed it. That was basically it. Then you waited for all of the enemy units to take their turns one at a time. It wasn't actually great. Since you could not control ANYONE else, you were mostly twiddling your thumbs because turn-based combat is not actually a good fit for a single-unit game with relatively low action complexity.
Fallout Tactics apparently saw how the combat actually kinda flopped in the original, so they made it real-time, and thus it flopped for the entirely opposite reason now that you actually had multiple units to control.
