So, people want to pay $15 and not interact with others, and that's a problem?
Nobody is stopping you from queuing with others. If they indeed went single player, they'd all be trust runs only, without a duty finder / party finder ability.
I don't see why someone wanting to play single player is a problem. Play the game how you want, so to speak.
If there was a single player version of the FF14 story, they'd probably play that instead, but there's not, so here we are.