It's probably more the behavior things. Keyboard shortcuts, focus behaviors, menu placement, file dialogs, etc. Settings panels in MacOs should take effect immediately, while in windows you have to click ok/apply... inconsistencies like this can lead to frustration.

But not doing this brings about an even worse kind of context switching—between apps on the same platform.

As annoying as it is to switch form cmd+C to ctrl+C when I go from Mac to Windows, it's even worse when a Mac app uses ctrl+C.

this, and also the need to write three (or four if you want to do separate stuff for KDE & GNOME) times the amount of documentation to accomodate for the different "default" behaviours.