Linux is big business for
Linux is big business for…well, big businesses. Much of the internet is hosted and organised through Linux machines, and there are companies which sell Linux support contracts to businesses who use Linux. Some distributions of Linux charge you (but most don’t), just like you have to buy Windows.
It’s a myth that Linux makes no money. It is true that it is mostly free (including most of the applications you’d want to use) for normal desktop users. Only if you have very, very special needs are you likely to need to pay for Linux.