Honestly, while that may be the case, I do think it partly stems from a lack of education, too. Most premeds at my university have no idea that PCA jobs exist at the hospital that they are eligible for or what the job even entails. Those that are aware tend to think that they're intended for only nursing students (partly true--nursing students are encouraged to take those jobs and can use them to transition it to a nurse externship and job after graduation) or would rather be a scribe because it's the classic job for premeds (and some don't want to have to take care of patients like a PCA does, but medicine is not the career for you if this describes you, in my opinion).
I do agree, though, that the way to fix the PCA market should not be to rely on a cheap labor farm from premeds. Premeds who do things just to tick off boxes tend not to do a very competent job at their activities compared to those with a deeper motivation.