Because they are idiots?
I believe that Michael Robinson will be, in fact, the Social Democratic candidate in 2020. He is not jumping in now because the early declarers are subject to all the fire and trashing of their rivals on the SD side and it would give the oppo research much more time to find disqualifying dirt. By the time he declares it might be deemed advantageous to declare his status as a Tranny.That would make for an interesting election, especially if (almost)open Communist DeBlasiio and Robinson are the two Last Men Standing in the primaries.
.