Why do people send you a message or anser your message then sign off and dont talk?

I'm going to make an assumption here based on your age and sex - you were trying to connect with somebody of the opposite sex and there may be people fitting those criteria on here but it's more likely that you weren't talking to one of them. I shall repeat my slogan about this; I don't believe anybody is real until I've had a pint* with them.
(And even then you can never be sure about real people's motives).

*Other beverages are available.