Indeed... malware devs aren't likely to waste time trying to implement malware for a closed ecosystem like iOS when it is likely much easier to find and exploit issues in an open source ecosystem like Android.
Especially given the market share disparity between the two
globally... Android a little over 70%, iOS under 30%, refer:
https://www.bankmycell.com/blog/android-vs-apple-market-shareAlthough it is interesting to note that in the US, iOS has ~57% market share.
In other case, using a wallet on your phone for anything other than casual day to day spending etc is likely a "bad idea"™... certainly not a place to be storing your main stash!