In January, Bandai Namco deactivated the PvP servers for the PC editions of the Dark Souls games after discovering a serious security vulnerability in Dark Souls 3. Bandai said the service suspension was temporary, but then updated in February to say that because of the time required to ensure the problem was fully solved, online services for the Dark Souls games on PC would not be restored until sometime after the launch of Elden Ring.
Six weeks after Elden Ring's release, however, there's still no sign of multiplayer returning to the Souls games—and in fact, it's looking like Dark Souls multiplayer could be gone much longer than expected, possibly even permanently. As first reported by The Outerhaven, all references to online play in Dark Souls: Prepare to Die Edition, Dark Souls: Remastered, Dark Souls 2, and Dark Souls 3 have been removed. They are now tagged as singleplayer games only.
The tags are gone, but references to online multiplayer options remain in some of the game descriptions. Dark Souls: Prepare to Die Edition promises "PVP arena and online matchmaking system [with] quick matching for players to play 1vs1, 2vs2 and 4 player battle royal," the Remastered edition offers "The Way of the Multiplayer (up to 6 players with dedicated servers)" and Dark Souls 2 features an "updated multiplayer system [that] enables improved online interaction to bring forward cooperative and competitive play."
You can see the change in the Dark Souls 2 page now, compared with how it looked in February 2019:
It's possible that publisher Bandai Namco removed the tags to avoid confusion or accusations of false or misleading advertising on the Steam page, but if that's the case it suggests that the security issues that came to light earlier this year, whatever they are, are much more serious and difficult to address than anticipated. Some fans, however, are concerned that it signals a more permanent state of affairs—that Bandai Namco is washing its hands of the situation and moving on.
I've reached out to Bandai Namco to ask what's going on, and will update if I receive a reply. In the meantime, if you're worried that Souls multiplayer won't be back, find hope in the words and forbearance of redditor bobface222: "Elden Ring sold 47 gajillion copies. That's going to be their priority for a while."