I think that everyone believes part of their job should include deciding both what they do and how they do it. I think it's pretty rare for non-managers in any field to have the latter, and extremely rare for any non-managers to have the former.
I'm not sure why you believe engineers would be uniquely entitled to make decisions about what they're building. Even in a classical engineering job (building a bridge) they don't get to go "nope, this is a bad idea let's not build it." At best they can say "this is what it'll take to do what you want, is it worth it to you?"
Really, deciding what to do is literally the only job top management even has. It's not often shared with the people doing the work.
I think the distinction between "what" and "how" is a matter of perspective. The "what" is definitely the domain of management (even if decisions are made with engineering input), but where the "what" ends and becomes "how" is fluid.
To use your bridge example, the "what" is "build a bridge" and the "how" is type of bridge, where beams go, etc.
That could just as easily be reframed as a more general "what" of "increase traffic capacity from A to B". The "how" might be a bridge, or it might be a new road that routes around the lake, a tunnel, or some other solution.
You could also frame it as more specific "what" of "build a suspension bridge" where the "how" no longer includes as many decisions.
You'd see the same distinction form between a micromanager and a hands-off manager. The former leaving almost all of the decision making in the "what" and the latter leaving almost all of it in the "how".
This is actually why so many organizations that are good at shipping other kinds of products suck at software: the distinction between "what to build" and "how to build it" is very squishy, and on a complex enough project the distinction is nonexistent.
A complete specification could just be executed. It is the program.
I'm not sure why you believe engineers would be uniquely entitled to make decisions about what they're building. Even in a classical engineering job (building a bridge) they don't get to go "nope, this is a bad idea let's not build it." At best they can say "this is what it'll take to do what you want, is it worth it to you?"
Really, deciding what to do is literally the only job top management even has. It's not often shared with the people doing the work.