While tryinng to generate FOMO is always a possibility, I think it's just that the social type stuff is just much easier to photograph because it's easy for people to be happy and smiling and look like they're having a good time. I don't know about you but when I'm doing the solitary stuff I love I just have resting bitch face (because I'm concentrating on what I'm doing and it doesn't require a reaction for the most part, unless I'm animating in which case I might be screwing my face up or repeating motions in the space next to my chair trying not to upset the rest of the furniture) and it doesn't convey the joy that I'm getting (though my anim attempts may provide some amusement for anyone observing both in the horrible mistakes that occur in the actual anim and in my cavorting).
Then looking at broader social problems (of people becoming shut-ins at best and self-centred sociopaths with overwhelmingly narcissistic main character syndrome so wrapped up int heir own wants and needs they absolutely cannot under any circumstances accept the fact that the universe does not and never will revolve around them) that might also be an underlying reason for trying to encourage some social leisure activity.
I just find the double standards of having fun alone and having fun in a group weird. Imagining yourself listening to good music and acting out some head fiction for a story you're writing or be inspired in your own personal workshop laboring away to make that fantasy have a corporeal manifestation. The time spent engaging in what you love without anyone's company and the joy it brings can just be as fun as an extrovert going out with good company.
A healthy introversion is still keeping a few friends and going out once in a while without other social impediments of course.
But the former (referring to introverts having fun) is less popular and probably going to be that shut-in loser with weird ideas until they make a breakthrough and make a hell of a money out of it, then they become the creative hero. I haven't heard of an artist from the old masters that were known to party hard, instead most of the biographies depicted as shut ins studying their craft and having fun.
From a purely technical point of view (of budgeting for and creating an advertisement that encourages people to look after their mental health by doing something they enjoy), extraverted activities are orders of magnitude easier and cheaper to make advertising material for which I think is most of why there is a ridiculously heavy bias towards that.
I do think it's extremely lazy to not cover small group/solitary activities but can understand why it's less done when considering budgetary constraints.
And another thought that just occurred to me partway through coffee #1, it could be that most/all of the people on the advertising teams are extraverts themselves and so are hyperfocusing on the ideas that would give them fun and don't have the imagination to consider any other type of fun.