>Because there are still unresolved pronouns in (Q2).
When something is self-referential and resolves to itself, that's the end of the recursive process. There's no need to produce a Q2 that is Q layered inside itself. You go and substitute the entire sentence in place of "this" and form some unresolveable chain of recursion but you do it for no apparent reason. If these were statements in a programming language your expansion might make sense, but not in the context of spoken english language.
I've updated the answer again with hopefully clearer examples.
You're getting stuck because you're used to only 1-level resolution/replacements for pronouns, because that's what we're used to in daily speak.
But I've given a concrete 2-level example, where you will question your own stance of "that's the end of the recursive process", and help you expand the logic to 3-levels deep, 4-levels, 5... to infinity.
Basically, OP has not provided a base case for his recursive question. As a result, it goes on infinitely, ending up in stackoverflow.