We boast over two million regular users of Ubuntu. Worldwide over 10% of laptops and desktops ship with Ubuntu (it seems the world can sometimes be considered to include places other than the contiguous 48 States, Alaska, and Hawaii). Dell, HP, and Lenovo all ship models with Ubuntu out of the box (Dell even ships them in the US). There are manufacturers who make systems exclusively with Linux (system76, Zareason) and the only way you can get a legal copy of MS Windows for them is to go purchase an OEM disk and install it yourself (good luck, installing Windows from scratch is a pain and not for beginners).
Microsoft obtained their near-monopoly in the US and Western Europe through a combination of unscrupulous business practices (for which they were taken to court and found guilty, with effectively no penalty) and sheer luck (their major competition imploded through their own bad management). They still have enertia on their side.
It's possible to not use Windows. I've never used it (except briefly as a professional doing cross-platform development). I've used Linux exclusively on my desktop, laptops, netbooks, and tablets since the late 1990s and soon I'll have a Ubuntu phone. I haven't had any difficulty doing any of the things most people do with computers -- including software development, music recording, and all the day-to-day things required of a manager in a medium-sized business.
So, what it comes down to, is that there's no reason not to use Linux. It's a choice, like driving a Toyota vs. a Ford vs. an Opel. Some people prefer one, some prefer the other. It's OK, it's a big world.