Why is GGG against more robust keybinds?

Diablo 2 had, admittedly, primitive hotkeys but even it is more advanced than Path of Exile.
Hotkeys in Diablo 2

In many ways POE encourages you to use fewer skills. Mechanically, linked and supported skills are often more useful than additional skills. I accept that. Something I have trouble understanding, however, is why POE encourages fewer skills through the UI, specifically by limiting how many can be binded. I understand limiting the hotbar but why can't I bind keys to quickly change my primary or secondary?

Again, I recognize GGG has good reasons for what they do. But I don't know what the reason is in this case and nonetheless would like at least what Diablo 2 had.