My sense is that A) some people don’t really care to help, they want to use the site for their own personal (and other peoples’) entertainment B) don’t know a legitimate answer, so simply answer a “joke” quip C) feel that a joke might “lighten the mood” even though that isn’t really the intent of the asker D) enjoy the attention that comes from getting lurve for a joke (like internet stand-up comedy). And yes, I typically think that unless a legitimate answer (or 10 have been given), jokes are disrespectful.