Apple has spent years teaching people that if it runs without modification, it's safe. End of story. It came from the App Store, or it's allowed by Safari, so it's good to go.

Couple that with malware getting more subtle [0], and Windows Defender getting better, and most people will assume they're virus free and have been for years (even if they're not).

[0] think cryptominers in the background and data exfiltration vs so many browser toolbars you get 3" of any given webpage at a time, and pop-ups on pop-ups