I would argue that there has been a diverse and diffuse audience for jazz since at least the 1990s. I can go into this if anyone cares, but most of you know what I'm talking about. Still, the total audience for jazz makes it a niche genre. Mosaic has catered to a niche within a niche.
Companies can get into trouble if they try to be too many things to too many people, but they can also get into trouble if they have a tiny customer base and do nothing to grow it. In addition to their box set approach, Mosaic could have diversified their strategy by producing compelling, standalone releases like so many other boutique labels have. And they really could have used some marketing help, in terms of where they sold, how they packaged their releases, and how they wrote about them. Their existing copy does not convey one shred of excitement, adventure, or - dare I say - fun.
All I can say is, I have a number of friends and family members who love jazz and who have extensive LP and CD collections. And none of them have a single Mosaic release. But, for 20 years or so, they have kept in business a number of other boutique labels who sell CDs at $20 a throw, who can write compelling copy, and know how to package and market their reissues.
Mosaic's approach may have worked for a brief period, but it is clearly not working now, as all the "How can we help Mosaic" posts attest.