Why does it say that? No game developer in their life would advertise that it's just odd thing to put on your site.

Enticing people into downloading malware with the promise of titties is common practice.

A bit of reassurance that the demo is a legit demo and not an attempt to infect your computer is welcomed by most sensible people.

Oddly enough, that's the one thing the real scammers never actually do. They just dangle the carrot and see who bites.

Also, some people have gotten false positives with their overzealous AVs.