They're either lazy or they can't get precisely the sort of answer they are looking for on other sites.
When it comes to factual answers, they should be able to do their own research. Some people are just too lazy to do that, or they may be hoping for personal engagement with someone in the course of getting whatever answer they seek. They may be kids feeling isolated or shy or something, and any engagement is meaningful to them.
Quite often, however, people who post here are looking for opinions regarding a personal situation or issue they've encountered, and mere online research isn't going to help them.
Finally, there are situations in which someone's asking for factual help that can't easily be found just by simple googling. You'd be surprised by how often I see questions that really do require some complex, not-at-all straightforward research skills or even professional knowledge.