Homebrew built almost everything from source back when everyone was already migrating to it. Fink and MacPorts being frequently broken was really the big driver, IMO.

As for why Homebrew packages seemed to be broken less often, I can only speculate. At least one big benefit it had was being on GitHub. A lot of folks were already familiar with how to cut a PR. Not so with how to submit a Portfile patch to the MacPorts Trac.

MacPorts has provided binaries for many years at this point.