Yes, however they are not doing it in consumer market but in enterprise. Their way of selling support (in way which is sometimes hard to extinguish from standard licensing fees) suits that world but it's pretty hard to do it in consumer space and mobile.

Company with very limited resources can easily be rendered obsolete by stronger parties who can basically take the project and ship products with enhanced closed source software bundled in. That's exactly what Google is doing with Android, now that it has become the "gold standard", more and more of their contribution is directed towards closed source parts which have significantly more features than their open source counterparts. It's very hard to see how company like Jolla could go fully Open Source and remain financially solvent.