Because the vast majority of users have no interest in learning how to safely vet apps and just want to easily use their computers and not worry about malware.
That goes for the malware on the App Store too, though: https://blog.lastpass.com/posts/warning-fraudulent-app-imper...
That goes for the malware on the App Store too, though: https://blog.lastpass.com/posts/warning-fraudulent-app-imper...