Of course they are, that's Apple's standard business relationship practice. See also why Mac's still don't have an Nvidia GPU option, because Apple & Nvidia got in some spat a decade ago and Apple has been holding a grudge ever since.
The more Apple brings stuff in-house the less this matters to the bottom line, but it shouldn't be surprising. Unless not having Fortnite begins to seriously impact iPhone & iPad sales, Apple isn't going to care regardless of whether or not it's hurting their customers.