bzr lost because it was poorly-architected, infuriatingly slow, and kept changing its repository storage format trying (and failing) to narrow the gap with Mercurial and Git performance. Or, at least that's why I gave up on it, well before GitHub really took off and crushed the remaining competition.

For my own sanity I began avoiding Canonical's software years ago, but to me they always built stuff with shiny UI that demoed well but with performance seemingly a distant afterthought. Their software aspirations always seemed much larger than the engineering resources/chops/time they were willing to invest.