Because some guys Don't know how good single life can be? lol they're crazy.. No, but seriously, some just don't like being single, some just need someone there for them all the time, or he may really like you and afraid if he doesn't make his move he might lose you to someone else.
I think there are two reasons a guy want to jump into a relationship. 1. alone and tired of being single, wants a relationship. 2. he really likes you and wants to tie you down to relationship. your problem is to figure out what he wants. 2 is a compliment if you like him. 1 could be a mistake.