He's focused on the critical path to colonizing mars. If an sustainable ecosystem becomes the critical path, he'll focus on it. There's so much else that is more important now though, and funding is limited.
There is a mountain of unknown unknowns in this problem - that it would expect would take at least decades to solve.
And unlike launching commercial satellites, nobody is going to be interested in dropping a few billion dollars on a biosphere R&D startup.
Doing that in orbit would be quite a trick, even if you didn't restrict yourself to only being able to use found-in-orbit resources.
Yes, no one is going to fund this until it looks like sustainable transport to Mars is feasible, which makes transport the priority at the moment.