It's not all about market muscle, even if this is a big part of the problem.
There is an area in which Linux is really lacking, which is "computer administration for dummies". Incidentally, the people who will be in the deepest trouble are home users, who are the administrators of their own computers, but have never learnt how to do that.
Grandma can use Linux: she will have a locked-down setup installed by her computer-savvy grandsons, and she only wants to go on the internet and print a few things.
Office users can use Linux, as their desktops are administrated by IT. Here the problem will be more about the OSS ecosystem. Almost every business uses "niche" software or "niche" features that are crucial to their operations.
But home users, who are always installing programs and configuring small things are in trouble. Let's say I run OpenSUSE... I can use YaST to configure my system. Or I can try to use the "system configuration" panel in KDE. Or I can use an independant KDE utility which will be happy to interfere with YaST settings, or will have absolutely no effect. Or I can use a command-line utility written in ncurses that I read about on the internet and was installed by default on the system (e.g alsamixer or others...). Or finally, I can hack directly the configuration text files, hoping that they have not been deprecated by a newer system.
If you know Linux, you will probably skip every of those steps to go to the final one, as it is the most reliable way to administer stuff with UNIX-likes. However, not every home user is either able to do that, or willing to learn that.
Let's compare the situation to Windows now, where you can go for 10 years with your home computer without even knowing what the registry is.