Because you were all dying to play this five-year-old game
I know, I might be the only remaining person who cares, but Borderlands (that is, the original 2009 title) is now playable online on PC again.
I recently got a few of my friends into the series via Borderlands 2, and some of them want to go back and experience the original as a group. Naturally, this all happened right around the time GameSpy was shutting down. 2K Games assured players that the online functionality would be migrated to Steamworks, but no specific dates were given.
In an update today on the Steam Community, it was announced that the migration to Steamworks is complete. I briefly tried it out, and all of the functionality is integrated into the Borderlands user interface; no Shift + Tabbing for the Steam overlay is necessary. There are even several public games being hosted already. Apparently I’m not the only one.