For the longest time the only way to get Fortnite on Android was directly through Epic. This really didn't hurt the availability Fortnite on Android. Apple side, considering Apples strict approach on application downloading their app store is the only "official" way unless you want to go through Apple developer signatures(which is a pain in the ass). Currency wise, I don't think this will hurt them either. Considering you can link your account and play on pretty much any modern platform, one could easily go on another platform and buy credits to use on any platform.