I say this as a roleplayer that used to run communities and has generally been involved in most of the major MMORPGs to be released over the years. Socialization in mainstream MMORPGs exists but not in the same way. It's by intentional design. The reason (in my experience) people say MMORPGs aren't social anymore is because modern MMORPGs are designed to be single player games with opt in party features. That's great for casual players but if you've never experienced an old fashioned community it's like it's a small village where everything has to be sourced locally otherwise you can't get it, so you have to make connections, you need to rely on each other, you need to make friends and outtings have to be planned. You need friends just to level! Your reputation matters. And everyone either knows you or you know someone that knows them. If you were evil good luck getting anything meaningful done! Modern MMORPGs don't really have that, they're typically mega-cities where people excel at apathy, personal reputation doesn't matter and everything is readily available or easily accessible at all times of the day, it's so insanely streamined -- atomized -- comparable to how it was that it's indescribable.
We've gotten to the point now where NPCs will soon be filling the party roles with it already starting in XIV, and likely WoW to soon follow. Even WoW which was casual for it's release was originally built from the ground up and designed in such a way as to force you to interact with other people. And it was destroyed for the sake of chasing after convenience and appealing the broadest (€€€) audience possible. The end result is that your average player typically treats another like a ghost. No one has any real intrinsic value in these games anymore. In WoW and XIV people even don't typically talk to form groups, or in dungeons, they just queue straight in to an automatic system, with a group of players they'll never see again, who are just a means to an end. Raiding is fun but that was always just one aspect of the game that requires serious cooperation, and now everything has been streamlined for raiding, by raiding, all the time. Because people like Ion Hazzakostas (elitist jerks, the forum) think everything should be balanced around a spread sheet rather than taking a hollistic approach. You know the most common complaint about there being no content? It might sound silly but you're meant to be the content, not just the dungeons, or the raids. Leveling then forming bonds to over come challenges was the major source of content. Not logging in once a week to do some dailies.
And I say this as someone that's typically very social, nothing leaves me feeling more jaded than the state of modern RP servers. XIV's Second Life scene which has attached itself like a leperous sore to the RP community, which its cannabalizing. Balmung used to be like a walking, talking, breathing village where people roleplayed out in the open. And everyone was incredibly friendly. Now it's Mos Eisley's red light district on a bad night -every night. Elwynn Forest in WoW used to be filled to the brim with happy, friendly, faces looking to RP and hang out. Now Goldshire is filled with people trying to groom children and porn addicted zoomers because Blizzard aren't willing to pay GMs to police community behaviour. (The same is true of XIV which is full of groomers)