An important part of this is that as far as I can tell, most AAA mobile games now ship all but the most fundamental "code updates" as updates to interpreted scripts/data files over the Internet, bypassing the App Store update mechanism. (Where does data end and code begin? That's a philosophical argument that historically Apple could look the other way on for high-performing mobile games with weekly or even more frequent event releases.)
Part of the calculus must have been that Fortnite was stable enough, especially from a low-level and netcode perspective, that it could do without needing App Store updates to remain cross-play compatible in the medium-term.
Part of the calculus must have been that Fortnite was stable enough, especially from a low-level and netcode perspective, that it could do without needing App Store updates to remain cross-play compatible in the medium-term.