Why Not Linux?

I have been working with computers for years now. It seems like everyone has heard of Windows and Mac (Apple), but few have heard of Linux...any distribution. I realize that Linux is the baby of the bunch being born in 1991 in comparison to Windows (1983) and Macintosh (1984). My point is that of the three Linux is free, stable, more virus resistant than either Windows or Mac, due mostly to a small user base, but also due to the fact that each application has its own little shell of programming so that if one application becomes corrupt all that one needs to do is reinstall it and then the virus is gone effectively making it simpler.

The issue with Windows is that all application software is in the inner-shell of Windows so that viruses can propagate more freely and Mac is similar to Windows in that respect. However, Macs use different coding therefore all that viruses need to do is use a different programming language to spread through Macs. So, now we come to the cusp of my question, why don't PC manufacturers use Linux given that its free, they could price the computers to sell and not pay for an OS and use that money to put more into computer design, or they could donate to Linux so that the code would get even better updates. Either way, why not Linux? As a stated before don't worry about viruses, less confusing software for end users, all that Linux really needs now is to make it easier to install applications, which it is due to the downloadable apps that install immediately just like when you go to the app store with an iPhone. Either way, Cheers! those are my 2 cents worth on Linux, if only it was more compatible with games...I would drop Windows in a heartbeat.