Jiggle physics aren't a new phenomenon. They've been around just as long as modern entertainment has been, if not longer. But, jiggle physics arguably more prevalent in video games, with the likes of Street Fighter VI's Chun-Li and the entire femme fatale cast of Dead or Alive's roster often cited as examples. Tekken too has its fair share of female fighters whose breasts are, for the lack of a better phrasing, out of control.
While it's easy to blame the former "issue" on Katsuhiro Harada, the long-time producer of the Tekken franchise, it appears the ever-vocal developer actually specifically asked not to incorporate jiggle physics in Tekken - to no avail.
In Harada's own translated words, he wanted Tekken's character movements to be more "serious and stiff" to stand out from other fighting games. However, much to his surprise, character chests started bouncing once the game was close to being finished. He adds that the, "programmers and modelers are probably secretly working on it together." Harada eventually relented after seeing that each title improved on the physics of the previous entry, explaining that the "muscles and fat started to sway more naturally with each work."
Breast physics in video games have become a controversial subject in recent years. The issue is often grouped together with the industry's still-unrealistic body standards, the improving but still lacking representation and diversity in games, as well as the sometimes purposely stunted character development and obvious sexualization of virtual women.