I honestly dont really see the problem - the game is supposed to provide you with game-content, not with a friend.
OP is mentioning things like trust and hardship to build a friendship on and claims that the game isnt providing any of it - I would like to add that shared fun is also a good basis for friendship (and that the game provides that) aswell as that I dont share the feeling that the game doesnt provides us with means to overcome hardship together and build a certain trust. I have built very close friendships in this game excatly through those - several friends and I are pretty much in snych in content and know that we will look out for each other (granted often not because the creatures in the dungeons are so terrifying but because the other people are...), but still. (A WHM-friend and I perfected our hallowed ground-benediction-cmbo, by just pressing the buttons at the same time and laughing about it for the next 5 minutes, wiping the whole raid)

People who want to socialise, will. People who just want to play this game solo, will. Both are okay (as long as the solo-people are fine with having a bit trouble in savage etc.) - you cant force friendships after all.

I also dont understand what one would do to tackle this "problem"? Make content harder and less appealing to solo player and punish them for wanting just two hours of gaming in the evening after 8 hours at their job, surronded by people?
There are plenty options to engage and interact with people, if you choose to do that - if you dont, thats on you. And for the people suffering from anxiety... I dont want to be rude here and I know the pain from it, took me long to get over it, I dont think a game should hold your hand through that (and at the end of the day its still up to you either way - the game wont do the typing for you after all).

The only thing I can think of would be an advertisment board or so for linkshells and FCs, to make it easier for you to find a community to fit in, if you want that. Other than that, I really cant thing of a fix - probably because I cant see the real problem to begin with. Or well, rather how its SE job to fix people becoming less and less social...