Apparently Sandisk did supply for Ipod Nano, but possibly not a big enough supplier for Apple tablets or phones.
With Anobit controllers, Apple does not need to depend on Samsung or Sandisk or Toshiba only for flash supply.
You'd think so, right? But apparently consumer demand is fickle. And Apple bought Anobit in order to keep its Flash in-house. So Sandisk has to compete with everyone else to get "the best of the rest..."