This software seems to never have been open source/freely licensed. That's not a bait and switch. They were giving you a commercial product, for free, and now have decided not to.
It's likely a case where maintaining separate builds for the free and commercial tiers was getting complex. Often times, this kind of software requires lots of manual reviewing and adding or removing modules, and they probably decided it's just not worth it.
I don't see how that particular line of thinking applies when: 1) They continue to have a free version for Windows 2) They continue to have a version for Linux
I just can't see that cost of having a free Linux version (on top having a paid Linux version) is big?