Because Twitter is about communication and conversations. And if someone unfollows you, it shows that they're not that interested in you.<p>I totally agree with reciprocating unfollows; I'll happily follow most (non-bot, non-spam) twitter people, because that's what makes Twitter interesting. But if they then unfollow me, clearly they're not interested in forming a communicative relationship.<p>Personally, I find it a little worrying that Twitter are dictating the use of their API: not in terms of number of requests (which they should be dictating), but what 'good practice' behaviour should be (which, perhaps, they shouldn't).<p>EDIT: I don't mean to sound so prescriptive; what I mean is that many people use it for conversations and communication; I understand some use it as 'RSS', and therefore - to these people - it doesn't matter if follows are reciprocated. But for those that want to use it to build relationships, auto-unfollowing makes sense.