Also, Wikipedia is able to make so much money from just donations because their target audience is "literally everyone."

MDN has a smaller set of users, and the thing with running websites with user-generated content is that it scales up pretty well. MDN probably only costs about a tenth as much as Wikipedia to run, but has much, must less than a tenth as many users.

Public Radio wouldn't bother me so much if they didn't also constantly run ads.

They have to sometimes because the donations (sadly) aren't always enough

It's more than "sometimes", these days. They've long moved on from a quick "this program made possible by..." to straight up reading ads on air, frequently. Between that and all the time they spend promoting their own programs, plus the pledge drives, I doubt their content/non-content time is any better than most commercial radio. Maybe worse.

The evidence says otherwise: They donate a lot to those organizations and use them heavily.