Why are philosophers these days so concerned with fleshing out possible rules for concepts (e.g., Crispin Wright's analysis of intentions)? Do they believe that people actually follow these rules? But how can that be if most (if not all) people can't even say what these rules are precisely? And wouldn't a more plausible answer be found in our being conditioned to behave in certain (imprecise) manners with certain words or phrases, much like, e.g., learning to use our legs to walk? If so, shouldn't this be more a matter of empirical investigation (on the level of science) than this sort of conceptual analysis?
I'm with Mitch and Peter, so far as what they've said goes. But neither of them answered your first question: Why do philosophers go in for this kind of thing in the first place? The answer is that philosophers who do go in for this kind of thing think that, if we could articulate the rules we tacitly follow in using the concept of intention, say, then that would be a way of saying what the concept of intention is , that is, of characterizing that concept. It is a much debated question whether this way of proceeding is best. Jerry Fodor, for example, has been arguing for some time that concepts simply don't have "rules" associated with them in the way Wright's project presumes. See his book Concepts for his most complete presentation of this idea.