I believe "Widely deployed platform" is the issue here.

A yummy target for virus and ransomware authors is a widely used piece of software: OS, browser, crypto library, Word processor, spreadsheet, PDF reader,...

Part of the problem is that in each of these categories, a single vendor often holds over 50% market share. As soon as a bug in one of those allow a RCE, that means millions of users at risk.

It's also true even if you don't run the software directly but use a service: memes that infect social media (see: Facebook and fake news) are basically viruses too.

Species avoid extinction from viruses thanks to diversity. Software users that want to stay safe should consider using the less popular alternatives.