The skill progression is atrocious

[Absurdity]

Not really. Number of active accounts is useless because, other than housing, there is nothing in the game that actively tries to keep you subbed, and housing is limited. Increasing total accounts means the interest for the game is still there. So as long as they keep making profit (preferably increasing profit) and interest is there (preferably high and/or rising), then that's what matters more for an ongoing service, regardless of the ups and downs of active accounts.

And I believe they don't count free trial accounts, so people have always had means to try FFXIV and see if it's a game for them, and even more so with the recent expanded trial feature.

You see it yourself, don't you? I'd argue player retention plays a not insignificant part in making profit. Interest doesn't mean anything if all they do is buy the game, make an account, play the 30 free days (at most) that probably came with the purchase and then quit.
They're not paying their monthly sub and they're not buying mogstation items, a.i. they're not making SE any more money.
And sure, SE might not do much to incentivize you to stay subbed and they might even tell you to take a break from the game but they still want you to keep paying monthly.