'git blame' is named after the subversion and CVS blame features that do the same thing. Subversion docs are clear that it's a snarky name and that 'svn praise' and 'svn annotate' are neutral synonyms.
Perhaps someone familiar with CVS can comment on its history there since it seems to be the first source control to add it.
EDIT: and one of the main reasons it's a useful feature is it tells you who to talk to to understand a piece of code, or to coordinate a roll back, or to do any other sort of communication. It probably matters more in a big company where code is changing frequently and you're unlikely to know everyone and what they're working on.