Comment by bscphil

> routers normally have uPnP enabled these days

From what I understand, uPnP took off for a while, but started to become much less common about a decade ago because of the security issues it caused. I think most routers come with it disabled by default now. (If you know of any surveys indicating otherwise, I'd be curious to read them.)

Part of it is that hole punching became a standard feature for new protocols, so the need to forward ports has been reduced.