I think chubot presents a pretty good reasoning in his documentation for oil¹. Basically I think it comes down to there being a lot of problems with bash scripts, but the currently alternatives to bash just introduce a different set of problems. With luck maybe one of the new ones will find the sweet spot, but we won't find out without people trying.

Still, if bash works for you keep using bash ;)

¹ https://www.oilshell.org/blog/2021/01/why-a-new-shell.html