It’s not. Not in absolute terms anyway, or at least not in every scenario. Window$ e.g. supports more hardware (and some HW it supports better), Macs have their super-sharp screens, etc. But Linux is different. Linux is free.
It’s free in every sense of the word, i.e. as in free beer and also as in freedom. Of course not all Linux distros are free, there are commercially available products, that might cost money. In some cases, you could purchase support, instead of the software itself. Some distributions might include software that is not freely licensed, yet you can find many a GNU/Linux system, that ticks both boxes just fine.
Freedom does not just mean some vague idea of being liberal. In the software world, freedom is well defined. There is even an organisation that takes care of matters of liberty. The Free Software Foundation or FSF defines free software as follows:
A program is free software if the program’s users have the four essential freedoms:
• The freedom to run the program as you wish, for any purpose (freedom 0).
• The freedom to study how the program works, and change it so it does your computing as you wish (freedom 1). Access to the source code is a precondition for this.
• The freedom to redistribute copies so you can help your neighbor (freedom 2).
• The freedom to distribute copies of your modified versions to others (freedom 3). By doing this you can give the whole community a chance to benefit from your changes. Access to the source code is a precondition for this.
You can read more about free software here. The majority of the world probably did not yet realise how much it owes Richard M. Stallman, but the Free Software community certainly does.
How is this possible, when Window$ or macO$ costs this and this much? It’s simply because the people, who are making it available, have from the very beginning donated their free time and effort, besides there are non-profit organisations that fund professionals who work on it now, and even commercial entities often show support. There is a lot of work behind this and a lot of people contribute. It is a fine example of a community project succeeding. (Besides some who make a good living out of it, which is an awesome career path.)
It is, of course, full of pathos, but more importantly, it enables anyone to leave their finger-/footprint. Really, anyone, after learning enough skills, can contribute. If you are not a developer, you can participate in translations. Whatever you like. And that is just about the coolest thing about Linux. The people make it together, for the people, and make it freely available.
Linux once was not considered pretty. Today you have desktop environments that are as good-looking as those of any other system. Talking of which, unlike in Window$ or macO$, you get to choose what your desktop should look and function like.
Sure, you might argue, that either macO$ or Window$ looks better than a particular Linux DE, but in neither of those will you get to choose the looks and workings of the graphical environment, and customise it to your liking way beyond just changing wallpapers.
Plenty of software
Choice can describe the approach to software as well. You can choose from many available applications for each task. Debian GNU/Linux alone has over 30000 software packages available freely. That’s choice at its highest. Sure you might not find everything you’re used to, but that would be like expecting Mac software to run on Window$.
Most applications will have excellent free alternatives, some even have commercial versions. Many distributions include appstore-like software centres so that finding software would be straightforward and easy.
Safe and secure
Yet where Linux truly excels is security. By design, (down to UNIX), it was a more secure system than Window$ will probably ever become (although some say it’s on the right path lately). It is more difficult to write malware and viruses for Linux, or so some Russian hackers did say.
Couple this additional effort required with the much lower popularity: the result is, people who write malicious code will be most likely to target Window$ systems (at least on desktops). This means that while Linux is not at all immune to viruses, it is a lot safer than e.g Window$s. (This, of course, does not apply to email phishing, and online threats, but those are not platform-dependent.)
There is a long-standing myth, that Linux is totally immune to all vulnerabilities, that no virus or malware would ever run on it, and so on. Some distributions themselves help to fuel the myth, advertising themselves, as being the safest possible way of computing, with no known issues. While that is not the case, as indeed Linux can have security breaches (which some bloggers/writers like to point out in a rather exaggerating, or sensationalist way, counting email phishing and other OS-independent security problems among Linux vulnerabilities just to make a point), the chances of “contracting an infection” are much slimmer than on Window$.
Being inherently more secure by design, Linux also offers specific ways to further secure or harden a system, many of which are simple for the end-user, while others require advanced system administration skills. That said, for the home Linux user those would be most likely overkill, and security should rather take the form of precaution (like not opening suspicious emails or visiting such websites) and staying informed while keeping their systems up to date with security patches. In short, if you use your Linux computer to do what most people do with their desktops, you will likely never know what a virus is.