They are falling into a misconception that everyone uses their computer like they do. An experienced developer will have common sense, won't use administrator account, will update their OS and won't do crazy things like typing "Watch movies free" to Google and click the very first site appearing.
Most of the developers won't even change their wallpaper.
So, you don't need AV if you can manage a gigantic code like Mozilla but it doesn't mean everyone is the same.
Ms antivirus is a joke regarding detection rates.