JMP is a subsidiary. When JMP became a subsidiary, the JMP part of the company became a separate legal entity, distinct from the parent company. This separation can simplify the sale process of JMP because the subsidiary can be sold without affecting the parent company's operations or assets.
Clearly, JMP's best chance of preservation is to be sold separately from SAS. Being a subsidiary makes that process easier. Perhaps that was the intention years back for making JMP a subsidiary.
Speculations as to why JMP has not been sold?