Offering only USB-C forces additional purchases and the resulting e-waste, so it's no surprise at all that Apple does this.
Is there loads of space in the display? Looks like apple is packing quite a bit into a slim display profile. Not to mention, ports with different dimensions/heights require additional fixturing and likely additional PCBs or connectors to work. It’s not as easy as slapping a few more ports in the display. Sure a company the size of apple can add more ports. But it’s far easier to line up 4x usb C connectors. And likely makes for less ewaste.
Personally I’d rather have an RJ45/Ethernet port built in over USB A ports. The monitor is going to sit on a desk it might as well be hardwired to the local network.