Probably because windows and Linux users aren’t searching for free Mac apps. While I agree that it would probably be difficult to implement an attack like this for Linux (partly because it’s Linux and partly because it’s userbase is generally more technically apt), Windows has been susceptible to viruses since the dawn of time because users just install random shit on autopilot and click through installers without checking what extra bloat is included (which is often malware disguised as an extra third party program). I don’t think I agree that this specifically is Apples fault. No one blames Windows or Linux distros for user error and poor security practices.
Google’s fault for not vetting the ads they let through? For sure. The users fault for not paying attention while installing the app and just clicking through the request to bypass Gatekeeper and then entering their system password when a pop up randomly asks for it for no discernible reason? Absolutely.
What should Apple do to fix this? Lock the machine down to the point where users aren’t allowed to have admin privileges on their own machine?