It poses a risk to personal safety, which is the biggest factor involved. Someone who gets ahold of your e-mail address, for example, could also get their hands on a lot of other information about you, and that is dangerous.
Ask is also not designed to be a social site, so sharing of personal information or arranging to meet with someone are not suited for Ask's Community.
The people in charge of Ask probably don't want a bunch of people becoming victims of stalking or identity theft on their website. Besides, this isn't really a social media site, it's a site for answering questions.