Old school vs new school
Moving from SVN to a DSS, I chose Mercurial over Git for a few reasons:
1) The command line of Mercurial is very similar to SVN.
2) The workflow is also very similar.
3) History is inviolate. What is committed is there, warts and all, in Mercurial just like SVN (and CVS before it).
The thing that I have never liked about git, apart from the complexity, is that history is a bit wibbly-wobbly and malleable. Now, perhaps I am a bit old school (I have been in professional software development for 25+ years) and am a little set in my ways (or, rather, like a lot of developers, am lazy and prefer the comfort of familiarity), but Mercurial just seems to fit the way I like to work rather better than git does. Sure, I can learn to do things the git way, but I'd rather continue as I am.
It's a shame, because I'm happy on Bitbucket. But now I either have to port all my mercurial repos to git, or move them elsewhere. And as others have pointed out, if you're having to port to git then there is no reason not to port *and* move elsewhere. I think Bitbucket have shot themselves in the foot here and are losing their USP. If they are going to be just another git host then why use them over another git host?