I switched because I had to nuke my entire Macports packages directory and start from scratch to fix one error or another several times a year. Got fed up with it and tried Homebrew ~3 years ago. Haven't had to do anything like that even once, so I've stuck with it.
Homebrew has all the markers of a project I should hate, but it's so rarely inconvenienced me in practice that I can't help but like it.
Perform an update or install a package, things break. Usually Macports itself would partially or entirely stop working. Not the same way every time. After the first couple times I learned that attempts to fix it usually didn't entirely solve the problem and/or took too long, so I just started deleting the whole thing and starting over when things went wrong. At least re-installing packages doesn't require my full attention.
2012 may have been around when I stopped using it, can't recall for sure. Maybe it improved after I dropped it.
Homebrew has all the markers of a project I should hate, but it's so rarely inconvenienced me in practice that I can't help but like it.