Square Enix have temporarily pulled the Mac version of Final Fantasy XIV from sale, after it launched on 23rd June in a pretty dire state, and with a set of incorrect system requirements. They are, at least, offering refunds for the game: you can head here (opens in new tab) to fill out a request form.
FFXIV producer and director Naoki Yoshida published this blog post (opens in new tab) on Friday announcing, and explaining, the decision to suspend sales of the game. It's a long, frank post, with a not particularly happy ending. There are complicated technical reasons why the Mac version isn't performing as well as the Windows one (it's also thanks to a development decision made to reduce costs), and while the developers are aiming to close the gap before they put it back on sale, Yoshida isn't hopeful that it will ever run as well as the Windows game.
They could have delayed the port until it was in better shape, of course. They could also have released accurate system requirements—Yoshida says that “in the chaos leading up to the multi-platform launch of our expansion, we released incorrect requirements, which were not updated prior to the Mac version’s official release".
On that issue, also from Yoshida's blog post:
"I believe that the biggest problem with the Mac version release was the significant discrepancy between the performance of the product our development team produced and the expectations our customers had for it, which was due to the lack of information available on our product when sales commenced, as well as other issues.
"[...] While the development and operations teams, as well as our entire company, were involved in this mistake, it was I who ultimately made the decision to release the Mac version under these circumstances and therefore bear sole responsibility, and I sincerely apologize to you all.
"Because of this situation, many of you purchased a product which your Mac hardware could not run at even the minimum system requirements, resulting in insufficient performance, for which many of you have expressed your dissatisfaction. Had we provided accurate information beforehand, I know many of you would not have purchased the Mac version, which is why we decided to offer full refunds. Once again, I apologize."
The above post goes into great detail about Square Enix's problems with the Mac version. They've pulled the game from sale until they can get it in better shape, and they can put together an accurate set of system requirements. If you've already bought FFXIV, you can continue to play, or you can request a full refund.