This is just on the follow-up question on the names.
Now, it is likely true that it is not obvious from the names/URLs what the difference is but perhaps this is also a bit much to ask.
Also, there was and in some sense is some discussion how to make the distinction more visible and some things might be done here.
That being said it is really not difficult to find out about the difference with some minimal effort:
It says prominently at various places that MO is a site for professional mathematicians.
By contrast it says that math.SE is a site for people studying math at any level and professionals in related fields.
This seems fairly clear. So, this site is for professional mathematicians only (not strictly in practice, but this is what is communicated), but some people that are not professional mathemarticians might still have some math questions, so there is a need for a site for those too, whence math.SE (and this is also how things actually happened historically).
And what kind of questions can one ask here, it says: research level math question So if you have any other type of math questions you cannot ask it here, or at least should not. Then on the other site you'd find a more welcoming description.
These two pieces of information are placed at various places on the site. I agree it should be still more visible, but it is also not hidden or only implicit.