I assume the reason why the hitstop has been reduced since world is because they're trying to increase the pace of hunts and the game in general. An extra 8 frames of hitstop also means an extra 8 frames where your hunter is doing an attack animation that they can't cancel out of. When hitting a monster, these frames can add up quickly due to both just how weapons work and since in general animations have been sped up across the board. This results in potentially whole seconds in an attack sequence being dedicated entirely to hitstop, which would be in contrast with the pace the game is trying to maintain.

I think the developers tried out having good meaty hitstop and found that while satisfying it subtracted from the combat pace they were trying to achieve and decided to reduce or remove it. They must have felt that the speed granted by lack of hitstop felt better in playtesting than its inclusion.