My understanding is that the controller is integrated into the SoC.

You can actually replace the storage on Apple desktops but it’s a bit of a pain and isn’t as cheap as m.2 2280 drives.

I don’t really know why Apple does this when their solution doesn’t seem to offer an obvious advantage. They aren’t faster than existing solutions or anything like that.

Vendor lock-in increases their profit margins. If people could purchase a 128GB Mac mini and install their own 2TB drives they wouldn't make as much money.