Jiggling boobs and related things like panty shots in video games have a long history, especially in Japan, going back to hand-animated 2D arcade games. I think it's just horny hetero cis male nerds designing and animating female characters and putting all of their fetishes on screen.

While I guess there's some initial basis in reality "boobs are squishy and would respond to movement" (at least if no bras are involved) video game boob physics have basically evolved into an artform of their own far removed from the real world. Gamers expect boobs to be big and to move noticeably.

It gets funny when everyone has the same exaggerated physics regardless of what they're wearing, like in this game. Even if a woman is wearing standard office attire with a blazer there's still a mini earthquake happening in her chest everytime she takes a step. The only exception seems to be full traditional kimonos worn with obis.