There's a great video from "Technology Connections" covering one-pedal driving here [1]. The gist of it is that one-pedal breaking doesn't have a great way to control the break lights, making it difficult for the cars behind you to recognize that you're slowing down, which can cause accidents.
[1] https://youtu.be/U0YW7x9U5TQ?si=7XFO_ZHIwUjd-3Sm&t=195