Compare selling on the App Store to selling physical goods in a real store. Can anyone just make a thing at home and take it to their local Walmart and demand they sell it? Of course not. There are quality controls. There are things you have to learn first — that your packaging needs to be in a suitable box, that you need to get a barcode, that it needs legal notices, etc.
If Walmart offered a “seller’s course” where you could go and learn how to do these things nobody would bat an eyelid. They’d probably be praised for it.
Here’s where my analogy falls apart, of course. Walmart still won’t list for sale the crappy useless thing that you made at home. Apple will.