There's a disconnect between the title and the body of this question, in my opinion. I'll address the title first, then the body.
How to learn from philosophy stackexchange?
The goal of this site is not in fact to be a source for people to learn philosophy; it is intended to be a rather specifically-focused tool which is relevant but not wholly sufficient to that goal. And per your comment that
the site seems to be functioning quite well as a question and answer site (lots of questions with answers),
it does seem to be decent at its job - it is a question and answer site!
- And even in that capacity it's of limited focus - not every philosophy-relevant question is appropriate here.
Similarly to how one can sometimes let the perfect be the enemy of the good, it's not always a good idea to try to do everything worthwhile; sometimes focusing on a single, limited task is actually a good idea.
It may seem odd that I'm harping on this so much, but this is an issue that has frequently arisen on PSEmeta, including if I recall correctly by the OP; so I think it is worth dwelling on.
Now as to the body of the question, you raise a specific point - that PSE answers could benefit from more references. I wholeheartedly agree with this. Better referencing is always a good thing, and certainly benefits a q-and-a site.
But it is important to view this in the right context, which is - again - that this site has a limited focus by design. So while in this particular case I agree with your critique, I don't think "it makes it hard to learn philosophy from this site" is generally an adequate justification: in this case the relevant point is that better-sourced answers actually improve the effectiveness of this site in its specific goal.