I may not care if some guy I've never met uses my niche library without attribution. (I do care, really.) But Microsoft certainly cares if you use their code without attribution, so why shouldn't I take the same belligerent, copyright-enforcing attitude towards them? That's the main reason why people are angry, because MS has "rules for thee but not for me" by virtue of being big enough to have ~~good~~effective lawyers and lobbyists.