Seems to be a catch22 for Apple. The more successful and ubiquitous it becomes, the more it will be targeted by the nefarious. All the more so because of the statistical affluence of the user base. That's a shame.
"Statistical affluence of the user base" + downloading a cracked copy of a £2.99 app = deserving everything they get.
We say the same thing regarding side loading questionable apps with possible malware within Android. Yet people blame Android. See what I did there?
I can see what you did, and another attempt at badmouthing Apple fails. The thing is, there are perfectly fine and safe versions of these apps are on the App Store. And MacOS X has GateKeeper, which the user can set into the "very safe" mode where it only accepts apps from the App Store, or into the "safe" mode where it only accepts apps that have been code signed by developers known to Apple, and the "unsafe" mode where it accepts any app, but only after giving the user a very very visible warning. So the user had to: 1. Deliberately search for a cracked version of the app. 2. Set GateKeeper to the "unsafe" made. 3. Install and run the cracked version of the app, against two very visible warnings that Apple gives you.