1. Movable Type is not free. Blosxom is. (This, in and of itself, is reason enough.)

2. Blosxom is simple, elegant, and functional; it was written by a perl hacker for perl hackers. I am a perl hacker. Movable Type, in my opinion, was designed for command-line phobic "ordinary folks" who are terrified of programming. As a result, it is bloated and overly complex to configure and use. If I wanted a pushbutton CGI interface to Blosxom doubtless I could write one ... only life's too short, and life's too short to be dependent on a browser.

3. Movable Type is so popular it's a routine target for comment spammers. If you need de-spamming add-ons, you waste time fighting spam rather than writing a blog. I haven't decided what comment system to replace QuickTopic with yet (possibly one I wrote myself a couple of years ago, that needs dusting off and updating with noindex hackery) but at least it's my choice. Whereas Moveable Type, at a software level, is a one-size-fits-all solution.