Suppose that instead of doublets consisting of lepton/neutrino flavor eigenstates, the sterile neutrino is a pure singlet with zero flavor. Then, since there would be no partner lepton for it to tunnel into upon switching up the weak interaction, it seems that the sterile neutrino, if it has any interaction at all, must interact exclusively through other interactions.
If there are four fundamental interactions, and nature doesn't necessarily generate a new interaction from a new symmetry, but sometimes merely augments the existing interactions with new dynamic symmetries, then it becomes plausible that; because the EM interaction is ruled out due to its connection to the weak sector; because gravity is far too weak to have any influence at microscopic scales, that sterile particles are strongly interacting.
If so, it could be the case that such an augmentation is uniquely a property of the strong interaction because there would be no reason to believe such an augmentation exists universally--hence; there are no selectrons, etc.
Phenomenologically, super-symmetry would never be any other than an approximate dynmanic symmetry since a sterile particle would eventually decay into a familiar quark/gluon combination.
Interestingly, it can be argued that the dynamic supersymmetry can persist over over cosmological time scales, while the the decay of the usual quark/gluon composites into sterile particles is much (much) slower than their decay by the usual decay mechanisms --thus explaining why sterile particles haven't been seen in earth based accelerator/detector experiments