It's mainly supposed to be simpler and by extension faster than btrfs (which is kinda proven by the fact that fewer devs made this thing work in less time when compared to btrfs). It happens to enable some extra features that way too.

However, while btrfs annecdotally had many issues, it's used by big players like SUSE and even bigger ones like Facebook these days. bcachefs on the other hand is nowhere near as battle tested, so I'll stay away from it for a little longer.