Their subscription doesn't count?
"Player retention" = fewer cancelled subs = $$$ for ffxiv
And the devs have made it pretty clear that they want the MSQ to be a soloable experience, and if being able to hide other players helps more folks who genuinely aren't interested in the social element of an MMO feel more comfortable trying it out, that's a fair amount of new $$$ also coming in.
I just don't see the point in yucking someone's yum when it doesn't harm you? And especially when it could be an active boon to the game.
The only argument against this is "but it's an MMO" which, yeah, so what? FFXIV will never be a solely singleplayer game, but that doesn't mean we need to shut down folks who are only interested in playing alone. This game brings so much more to the table than just its social elements, and it would be a shame to gatekeep that from solo players just because they want to play solo.