I remember when they became standard way to select weapons, abilities and so on in the Xbox 360/PS3 generation and how modern and next-gen they felt. When you wanted to change equipment in older PS1 or PS2 games, typically you had to pause the game to dig around in an inventory to pick a new weapon, then exit back to the game and oh boy does it feel clunky when returning to those older games.

I assume the change was motivated partly by the dpad finally being completely supplanted by the left analog stick for movement so designers could come up with new uses for it

PC games had of course used the number keys as hotkeys since day 1 so the change was mostly a console thing