On behalf of all PMs, I'm sorry you had this experience. Good PMs tend to do just the opposite. If you are in this situation now, I encourage you to share this feedback to the person that is most likely to help change it (ideally with the PM directly?).
As a company scales, there is a tendency to embrace specializations through a division of labor. Of course, different companies adopt different models for various reasons. e.g. Do you need dedicated QA or does that fall upon the developers? With these decisions come trade-offs because you can't optimize for everything. Your proposed model can work, but is far less common in large tech companies because of the overhead of coordinating/communicating across lots of people which tends to fall upon PMs.
As a company scales, there is a tendency to embrace specializations through a division of labor. Of course, different companies adopt different models for various reasons. e.g. Do you need dedicated QA or does that fall upon the developers? With these decisions come trade-offs because you can't optimize for everything. Your proposed model can work, but is far less common in large tech companies because of the overhead of coordinating/communicating across lots of people which tends to fall upon PMs.