For me, free as in freedom is the primary concern. A proprietary programming language seems a bit ridiculous. I don't see myself paying for a programming language either, though. Libre and gratis are the norm in this space, so going against that sticks out in a bad way. It's like text editors and web browsers. We've had good free options for a long time. Anyone trying to push a non-free option might as well be giving out malware. That malware isn't appealing whether it has a pricetag or not.