Because muscle memory breaks if the physical layout of the keys is different. The parent is used to ANSI and might hit enter where there's a different key on ISO. I am used to ISO and my layout uses that key as a modifier and is barely usable on ANSI, simply because moving my pinky to the key above enter is uncomfortable for me.

It is not possible to "just map": Enter key has completely different shape and size and pushes backslash/pipe key to different row. I'm used to ANSI with single row Enter and I don't seem to be able to switch to ISO (in the past I was forced to order and replace keyboard in my laptop because of that)

Exactly. They even offer a "complete black keyboard" with no letterprints at all - definitely aimed at power users.

The difference between ISO and ANSI is the physical layout, i.e. the shape of the Enter key and the left shift key.