I don't understand the Fifa split. Last year you could say it was the small install base and the first game of its ilk, but with the great legs it got you'd think it would start stronger right away this time. It's like we're back to square one.
Maybe the people who bought it a few months ago don't want to pay full price for another low effort stat update.
If EA had used the money to get Frostbite ported or at least do something unique with the old engine, perhaps sales would have been higher.
Also there is the possibility that buyers of Switch FIFA are content with 18 it and will just keep playing it regardless if there is a new version.
Time (and legs) will tell.