When I talk about selling software to GNU/Linux I mean the normal consumers, not the enterprise.
The enterprise is relatively easy to sell software to GNU/Linux users, because what gets sold is actually training, support and consulting.
All things that non-technical consumers don't care to pay a dime for, but they usually buy shrink-wrapped software, even if on digital form.
I remember circumventing FlexLM on SGI machines with IRIX and Nokia N810 with libfaketime and LD_PRELOAD.
I believed back then, and still now, that money is to be made with experts & service. Seems to work very well for companies like RedHat and IBM.
If you look at the engineering workstation segment, there are companies with hundreds or thousands of seats pooling FlexLM licenses of very expensive software, namely for microelectronics design.
Those seats are typically RedHat or CentOS. If you look up revenues for Cadence, Mentor and Synopsys, most of it is EDA software licensing (remainder is mostly IP and training.)
Not prime time news, but not pocket change either.