I think it's more a matter of discipline than anything else. It's easy to get lost in the weeds with a ton of things waiting to be merged, and over and over saying "just one more PR to merge and then I'll release", and then it's a year later and you still haven't released.

Getting features out to people faster means shorter feedback cycles.

Regarding versioning, most applications don't use semantic versioning; that's mainly for libraries. Not sure what "backwards incompatible" would mean for a browser, anyway.