The DO doesn't care about them. Moridin I believe is his proxy. And, Moridin knows he doesn't care, and understands his role. He knows the DO doesn't care about him and he's fine with that.

Moridin is the true Nae'blis, if such a thing really matters. He's the DO's most loyal servant and by his own beliefs he'll have to face Rand at the end. He's the counter to the Dragon, if you will.

If the DO gave the title to Demandred, he and the other Chosen would care.

Moridin wouldn't. Demandred was the general back in the War. Moridin never really was. And, Demandred was likely freed shortly after Aginor and Balthamel. Yet, Ishamael was already the highest. And, upon his resurrection, he was there again.