Linux is open source so you can tinker with it however you want, its codebase can be found on GitHub. Some people (like me for example) run a "custom kernel", that basically means that You have configured the linux kernel manually and built it from source, a lot of binary distros don't let you do that, but source-based ones like gentoo let you do close to everything - including, but not limited to, having a custom kernel.
Linux is open source and has many people looking for bugs in linux everyday. The bugs get patched quickly and we in return get a more secure kernel and so - an operating system. And as it's less popular among desktop OS world, there's not a lot of people trying to make malware for it.
Linux can run great on old hardware because it's not as bloated as windows or macOS. People have even managed to run linux on a literal potato.
Linux is easy to hack (as in change/modify) and it has great package management and together with that most programming tools and languages support linux better than windows or any other proprietary OSes.
You can control when and how you update, when you reboot, etc. linux is yours, nobody is in charge besides you. It doesn't randomly and painstakingly update after reboot, you usually upgrade through you package manager - for example apt for debian and debian-based operating systems on top of linux.
In linux we have loads of window managers (WMs) and desktop environments (DEs). You get to choose what you install and DEs nor WMs don't change as much as windows UI. They're mostly open source so also really hackable and lighter than windows. And WMs are really lightweight so great for old hardware.
In linux we have a lot of distributions with different use cases and features, for example: - Debian - stable - RHEL - server/enterprise use - Gentoo - hackability and customisation
Linux is free because it's open source. Linux gets support from optional donations and community support.
Linux has a good, knowledgable community so if you run into an issue You will have good support and will probably solve it pretty quickly.
Linux is private, it doesn't spy on you nor collect any data about you just to sell it to companies and from linux came linux-libre which is even better in privacy.
Linux supports a lot of architectures and computers so you can run it on basically everything, unlike windows and macOS
Linux is easy to debug and solve issues with, unlike in windows where you just get a random blue screen with a ":(" and don't know what to do.
Linux doesn't restrict your abilities - everything is possible
There are loads of other reasons, but I'm getting tired so - have a good day and consider using GNU/Linux(-libre) as your desktop operating system :)