You are basically stating the opposite while completely ignoring the actual complexity of such an hypothetical merge for codebases that forked 15 years ago. They share a kernel and some API, but on the UI side recent cross platform framework are more like a proof of concept than a production ready thing.

[1] not actually hilarious

Them pulling ill-suited features over to macOS, like the Control Center[0] and toggles, also give me pause.

[0] Which lives in the menubar, lacks any keyboard accessibility, and introduced bizarre new interface behaviors, e.g. multi-step dropdowns where you click inside the dropdown to navigate back. Ugh.

Most of the same people that fear the convergence also ask for "iPadOS" and "iOS" to be more like the Mac (add mouse support, multitask like the Mac, and so on).

So what they do fear is the mythical "dumbing down" of Mac, as in the outcry when Logic got a different skin, and everybody losts their minds as if it's now "just Garageband Pro" (meanwhile it has never been more powerful). Same for FCP (where a few features were lost due to the rewrite, not for any dumbing down).

Not sure why you see it as an irrational fear. What timeline are they actually working under / how are they prioritizing that convergence? I don’t know but it’s clear it will happen. I’m sure there’s a lot of unification going on of background services (radio stacks, security hardening, etc) in addition to more visible UI pieces.