They don't, and should. The problem is that these are not easy questions. Almost no program at any undergraduate institution has the depth and rigor that would allow anything but the flimsiest, least-informed questions or answers of this sort.

"Is our current economic system even sustainable" requires a understanding of value, international trade, global distribution of resources, especially nonrenewable ones, an understanding of history and previous (wrong) predictions to help keep us from making the same (bad) predictions again, a basic conception of the physical basis of climate change and the extant technology and possible future technology to address it (in enough depth to actually think through the feasibility of employing it at scale, and again keeping in mind the errors of history), etc. etc..

This is a massive undertaking. Maybe you just mean the question should be asked aspirationally. "Wouldn't it be nice if we could answer a question like this!"

As an undergrad, I took an environmental studies course that did try to address these questions. Despite a pretty good background, it was quite obvious to me that we students had no way to know anything beyond what other people were telling us about the big questions. I spent a lot of time researching glassification of nuclear waste for a class project, as one small corner of the feasibility of nuclear power, as one corner of less environmentally destructive power generation, as one aspect of an environmentally sound economy, and after dozens of hours was barely informed enough to say sensible evidence-based things (which, incidentally, were way outside of my professors' knowledge).

If you want students to actually have any informed ideas, they need a solid grounding in economics, earth science, technology, history, and human psychology. Counting reasonable prerequisites, you might get there after 10-12 courses.

This would be awesome. But it would be much less easy than universities let students have it now. (But maybe the students would be more motivated.)