curiousdannii has done a good job explaining that this site is about the FLOSS community, including history, philosophy, and cultural norms. We accept licensing question only insofar as they fit in with the site's scope of FLOSS in general.
Part of what practically distinguishes us from http://law.stackexchange.com is that many open-source licensing questions can be answered without any legal background, simply because FLOSS licenses usually have have extensive public FAQs. When you're answering a question about an open source license, the first thing you reference, usually, is the official word from the creators of the license (e.g., the GPL FAQ, Apache FAQ) and then jump into legal mechanics if the question is too nuanced to have been already addressed. This is not an accident. Tying in with the paragraph above, it is strong cultural norm in the FLOSS world for license authors to provide extensive, plain-English explanations of free and open licenses, which is by no means a norm in the world of licensing in general.
Helping people understand what FLOSS licenses allow and require is a tradition of the FLOSS subculture; it is a tradition that began before this site existed, and which the site's users now participate in. When we answer questions about FLOSS licenses, we also consider the publicly stated intent of the author (e.g., "the text of this GPL section might be understood by a judge as causing either X or Y, but the spirit of the GPL is clearly X"). When we answer licensing questions, we can directly contact the license authors and get back prompt replies, because they are interested in having their licenses clearly understood.
We could expand our scope to include all licensing questions, or include, somewhat arbitrarily, questions about licenses which allow recipients visibility of the source code (non-free "source available" arrangements), but I don't see any benefit to doing either. With the first option, we'd be directly competing with Law Stack Exchange, and with the second option, why should we choose to draw an arbitrary line at only licenses that allow recipients to read source code? What's the point of that? There's no specifically identifiable community that would be better served by that arrangement, whereas our current arrangement serves a very well-defined community.