[nostrademons]

Broadband and wireless routers kinda killed this. It's now typical for every computer on your home network to be behind a NAT, so to enable direct connect, you need to manually punch a hole in your router's firewall. The spyware situation of the early 2000s (which caused Microsoft to bundle a personal firewall with WinXP) didn't help either. Most users are not willing to fiddle with their network connection just so someone on the Internet can directly connect to them.

[lastofus]

WebRTC allows for a peer-to-peer data channel and does the heavy lifting of NAT punch through for you. I've mostly been messing with the video chat side of things recently, but would be curious to see if the data channel could be used for large file transfers.

[nostalgiac]

Hardly killed it. There's a reason UPnP exists.