Price is the major issue for me. I'd love to use one, but the same amount of compute power is available from big-brand manufacturers as low-end servers in the x86 space. It's hard to justify spending extra for a different ISA.
Raptor is well aware of their price premium and tried very hard with the Blackbird, though I wanted the expansion power in the Talos II and would have always bought the bigger system first. But they still have to make a profit and I want to support them in it.