Yes, but this doesn’t answer why I only have to do this on Mac and not windows/linux, where I have literally never run into an issue as a result of not doing it.
Windows and Linux both ask for your language and locale during setup and default to the typical matching keyboard. I'm nearly sure Debian also asks you to confirm the keyboard it picked, but it's always the right one so I just hit enter.
If you're using a US English keyboard layout, it's the default and you won't have to deal with changing it.
The most likely reason it would be a problem then would be that some Raspberry Pi images have defaulted to British English keyboard layouts. Otherwise you may be sailing through life unburdened by what can be a major pain to anyone anywhere else in the world, like a resident of Arizona wondering why the rest of the world keeps messing with their clocks.
Do you live in a country where the default always maps correctly? My UK keyboards will always have specific keys wrong.
I assume you have a standard US keyboard.
I assume for some nonzero percentage of folks it doesn't work right and they have to manually go and set their keyboard layout.
Of course, when you're setting up your OS initially, it will ask you questions about language and keyboard layout. I suspect most people don't switch keyboards after install, and of those who do, the most common case is another keyboard with a compatible layout.
Most non-Apple branded keyboards are NOT tested with mac; so it doesn't trust any electronic tags/labels, nor does it keep a database. Easiest thing to make it work 100% without asking the user to identify their layout, is to press random keys so the mac knows where things are mapped.