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.
Nobody is going to fund it after sustainable transport to Mars is feasible, either. Because there is no path from 'spend billions of dollars on this' to 'make your investment back'.
Which is why IMHO the next logical step is to establish orbital autonomous manufacturing. There’s no way an experimental artificial habitats can be built on Earth by manual labor let alone launched by chemical rockets.
Note that manufacturing anything useful to our technological society currently requires a supply chain of tens of thousands of factories, worked by millions of people, requiring mountains of input ingredients, and producing mountains of waste.
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.
Aren't Elon Musk and Jeff Bezos both interested in this and their combined wealth around $200Billion? Seems like they have plenty of money to throw at this company even without outside investors/governments.
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.