I was recently looking into surfactants, albeit in relation to polyquats, but found this thread extremely helpful:

Cones, polyquats, ions, and removal of buildup

Basically, dimethiconol is a water insoluble cone that cannot be removed by nonionic surfactants. You need to use an ionic surfactant to remove it (or something harsher).

I have only checked out two Shea Moisture shampoos, but they both had decyl glucoside, which is a nonionic surfactant. That won't remove the water insoluble cone. Cocomidopropyl betaine is an ionic surfactant that will remove dimethiconol. The thread above provides a much more thorough explanation, though!