Ah, you haven’t read far enough back in the archive here:
https://community.gotennamesh.com/t/mammoth-mountain-ca-ski-areas-now-fully-meshed/1897/22
Most ski areas are like other organizations that serve the public. They respond to requests from their customers. When you hit the slopes, ask about whether they have goTenna Mesh coverage. The more who ask, the sooner this will happen.