There are many reasons why Linux/GNU operating systems are not going to be as popular as Windows systems for some time to come. Maybe 5 years. Maybe 10. maybe 20. Hard to say.
First of all, a lot of professional commercial software does not run on linux. It could run on it, but as Kulver has said, companies can't be bothered to spend lots of money to port their software.
Good example of a niche where pros choose win/mac over linux is motion graphics/special visual effects. Both win/mac have professional solutions, where linux has only entry level basic software in that niche.
That is just an example.
Another good example would be games. There are so many games that you just can't get working on linux. And companies wont port their best games to linux because the linux market is so tiny. Also, linux doesn't have decent drivers for many modern video cards. If you read through linux forums you will see countless threads about how people are having problems with getting video cards to work properly. Yes most of those problems have work-arounds, but for a simple guy who is not into tech stuff, even that simple problem might take a lot of time to solve. This problem should go away in a few years though, as manufacturers are starting to take linux more seriously and start making drivers for it.
Also, the benefits of linux (better security features, more efficient kernel, less crashes) might be less relevant to an average user who just uses his computer to browse the net, use photoshop and play some games. After all, in order to secure a linux system properly, you need to do some work. It doesn't come super secure out of the box. That is just an illusion many people have.
The only advantage for a normal user would be the cost and less viruses/malware. And disadvantages would be spending time to get used to a new system, spending countless hours trying to get things working properly, some of their favorite software not working.
And talking about malware, there is a very small risk of anyone who just follows a few simple rules of being harmed by malware or viruses. I have been using computers intensively since I could read, and I have never been harmed seriously by viruses/malware. No one ever got my email account or stole money from my bank or anything like that. And if they did, I never noticed.
So in short, there is just no need for most people to start using linux. I use both. When doing anything tech related like coding I use linux. Just because I am used to the tools and the environment and I can operate the linux tools quicker then equivalent windows tools. But if I want to play a game with some friends or do some graphics work or something casual like that I use windows. Never had a crash since I installed it.
So what I am saying is most tech people are obsessed with linux and GNU/FOSS stuff. Yes its cool. Yes its a better way to do things. Yes, its probably the future. But at the moment, for most average people its just easier and quicker to stick to windows/mac for some time until some things in the open source world change.
No need to act like a cult.
