[gregcohn]

Assuming you're applying the appropriate effort over a large enough sample, which it sounds like you are, then the logical possibilities are that people either don't want to make friends, generally, or that people don't want to make friends with you, specifically.

The first one seems more easily tested -- for example, it can be disproved if other people are making friends under reasonably similar circumstances. It may turn out to be the case, however, that you're aging into life phase in which people are generally less inclined to buddy up. If this or some other issue is the case, you may need to change the conditions -- e.g. move somewhere else, seek young friends, etc.

If you begin to suspect it's the latter (people don't want to make friends with you specifically), then what you want to get is some honest feedback so you can evolve into an easier-to-befriend person. The good news is, a little self-awareness goes a long way.