Profiling :P
in therapy you don't expect to be judged. well it the superficial everyday judging way :)
with random strangers, there are probably a plethora of reasons.
first and main is probably the "i will never see this person again, and this person will never see anyone i know"
one is certainly just the human nature of "hmm someone is interested in my story, not sure why, but lets try to make it an interesting one" :)
one can be that it is cheaper than therapy :D