For me, the base OS must remain free (at least mostly), the software can be proprietary.

It's easy to move to different software, it's difficult to switch platforms. You need a platform you know you can trust.

I'm on Linux because I like the experience and the control the base OS gives me. I still need my tools to make me money, and I pay for plenty of software that makes my life just a little bit easier so I can turn in work quicker and make a profit faster. Business expense.