FFXIV for macOS?

[Lemage]

Why do I have to pay for the game again when I've already paid for it

You don't, the Mac OS client is just an excuse to toss a wine wrapper and charge again, just DIY.
Linux similarly has the option to use Proton.

Edit: I realise this is an old thread, but this is directed to anyone who is wondering, not just the OP.

[Bruenor]

Thanks for necro'ing, seriously. I was shocked I had to buy both versions as the MMORPGs I had been playing since 1999 were either Windows only or buy one download both (Like WoW).

Since my new mini has no GPU I had been going eGPU but cant justify the expense since I have a SFF tower with a half height 1030 in it. I sure didn't want to add another $70 on top of the eGPU for one game. I have used wine though, so if that is all it is, and it works with an eGPU, that "could" solve my issue with what I want to do.