Why is the micro sd a problem? It was there on the early pi (as a normal sized SD slot) since it was cheap, easy to implement and widely available. And the chip

Why is the micro sd a problem? It was there on the early pi (as a normal sized SD slot) since it was cheap, easy to implement and widely available. And the chips could not boot off usb so there was that. These days I guess it is mostly for legacy purposes and the pi can boot of usb anyway if you don't want to bother with it.