Call me crazy, but I am pretty sure most high schoolers aren’t all that knowledgeable about the job market. If they were, we probably wouldn’t have so much to discuss on this site. High school students selecting a major are not what drives the enrollment numbers for various majors at universities. The universities themselves do that, generally based on how many people they can actually support combined with how many they think can reasonably find jobs (after all, it looks bad on the program if half of your grads aren’t getting jobs). There are also far fewer aerospace programs nationwide that, say, mechanical or electrical programs.
So, the reason there are fewer aerospace engineering graduates is because there is less of a demand for them nationwide across all industries. Within the aerospace industry itself, they are still very much in demand, as well as in specialized roles in other industries such as automotive and wind energy. Basically, nearly all aerospace engineers work in the aerospace industry, while mechanical or electrical engineers (or most other flavors) work in much more varied industries. That’s hardly the same thing as being unmarketable or unemployable as an aerospace engineer. There are still generally more positions available than graduates, just within a smaller niche in the broader industrial landscape.