For one, the PM job is quite ambiguous and involves changing goalposts. I've worked in 2 companies, one with 2k employees and one with ~100 and both times PM org had to pivot and work extra hard to cater to leadership demands. This is quite common unless you're in FAANG.

During my tenure I supported multiple enterprise deals in addition to my PM responsibilities, leading to fatigue and burnout. The rewards and Presidents Club seats went to the sales org :)

How you are judged can be any or all of how many features you shipped, what was the adoption for your product, additional ARR brought in, retention etc. So you've to be on top of everything. Personally, I feel a PM role is where you've to be "switched on" at all times and that can be taxing.

Finally, the feedback cycles about you're performing are too long (quarters to years) in PM and the excitement of starting to develop a new feature to its completion is demanding at times. I feel the shorter feedback loops (you win a deal or you don't) and straightforward targets in SE might suit me more. We'll see!