My reasons are:
- That it keeps away viruses
- It is easy to run applications like web servers without affecting performance for testing purposes.
- It is very very stable.
- You don't have to reboot to install updates.
- There are forums for support if you are unsure about how to fix something. you also have access to the whole system and if you really would want to you can rebuild drivers from source code. I have done this for an old laptop before because the standard kernel module did not fully support the bios interface for my computer (that was not following standards).
- Everything is free!
- This also means that everything is free in your software repository, so with one command you can install a whole bunch of software quickly.
- Automatic de-fragmentation of the file-system. In windows the file-system in time gets fragmentated which means that files are split up in several different locations. If you are on a standard magnetic harddrive this becomes a real issue after some time, depending on how you use the harddrive.
- Very well structured operating system, you can understand as much of it as you like. It is possible to change everything. But be careful, you may, and most probably will break something if you try to be root all the time like an administrator in windows.
- If you learn Linux, you learn skills that are transferable to for example UNIX systems. You will be familiar with a whole lot more computer systems when you learn Linux.
- Old hardware-support. Linux does not stop being compatible with old hardware like windows sometimes is.
- There are continuous updates for everything. Because of the software structure, it is, as long as every application in your distribution is a free open source version, most often possible to update as soon as the software has been packaged and tested.