Its not that, I love the Sword Coast work. Its just I've been mapping modules to their position on my interface world map of Toril and after some research on FMA1,FMA2, FMQ1 I realize that they are ever going to touch Maztica again and I find that a shame.
So, three things and a related point-
1. The above was a joke. Kinda. That said, if you're a fan of pretty much any other setting, listening to FR Fans complain about FR material is kind of like listening to comics fans complain that DC doesn't do enough with Batman. Sure, Batman might be cool, but pretty sure DC does a lot with him.
2. Maztica (and certain other settings) present various serious issues that are not present with other settings; in effect, the risk/reward ration (in terms of risk of screwing it up as opposed to likely sales) makes Maztica a tough one to justify. No matter how well they do it, someone is going to complain, and it was never a super popular part of FR.
3. There's a lot of legacy material out there if you're looking for lore, and some good 3PP for 5e as well. You're covered if you want to be. I know it's not official, but it's good.
Now, as a final point- I happen to agree with most people regarding the Grey Box. To me, that is still the best FRCS. I understand the lore completists- if you're into the books, and the videogames, and the "FR Story" then that's cool. But in terms of an RPG campaign setting, it's often best to be sketched out, and allow home campaigns to fill in the details. IMO.