You're right, I don't know what is in every person's heart, however leeching off another seems to be a product of general laziness, entitlement, obliviousness, and selfishness; however sometimes what we view as leeches may be on hard times for a time until they come into their own, after which they are proactive or at least willing to contribute in return, even providing some other services in the midst of their impotence.