Because many users have no idea on how to find out what things are available and what's popular, and/or even that there might be aggregators of this info, or the concept of such.

Observe how many people do not even do a search for very simple things. The concept that they might be able to know or discover certain things doesn't seem to actually occur. Of course, this needs to be distinguished from their just being lazy, but even this is problematic, since it's almost always the case that finding it themselves is much faster than asking someone else (who will often essentially just do what the asker didn't...). It's almost a kind of learned helplessness, but with the "learned" part often being very short or implicit.