Gaming companies contributed to the death of LAN parties too. They killed the "split-screen" gameplay that would support 2-4 players on the same machine. They wanted each player to require their own copy of the game. They killed LAN support, forcing you to play on their servers. Culturally we saw a shift towards social isolation. People are more comfortable talking over a mic.
Gradually the companies figured out how to inject themselves into the social structure. Your relationships became mediated by these products. Rather than a social lubricant they became the relationship itself. They monetized that social capital.
You didn't play WoW with your friends anymore; you played WoW because that product allowed you access to your friends.
Some superguilds figured out how to hop games and maintain that social structure, but only the most organized and intentional. Gradually these LAN groups eroded as people got jobs, families, etc. Perhaps that was why the MMO declined; those friendship structures became compromised by the product, and people also developed constraints on their time by things like, spouses, children, and careers.