I think people are quick to dismiss FF14, because it was never as popular as World of Warcraft...
But people forget theres still like 14-15m players playing FF14.
Its not unreasonable to see the playtime cards doing well on amazon.
Actually Square Enix revealed not long ago that they had 16M players registered all time since 2010 just a month ago. Not sure if Square ever released any active player count but according to https://ffxivcensus.com/ there's roughly 670k active characters worldwide.
So while I dont know how legit that website is, there's not 14-15M currently playing the game based on Square Enix numbers alone, but the game has increase a ton over the last two years and is very much in a super positive trend since the last expansions.. especially compared to juggernaught WoW who has kind of been in a dwindle after BFA released.