New standards take time to gain traction. Apple putting at least one USB-C on each "new" device would go a long way towards helping USB-C gain adoption.
I think they should have 'burned the boats' and gone all in with USB-C on everything they have updated so far (I.e. MBP 13/15, iMac). Throw a solitary adapter in the box, charge a nice Apple margin on additional ones.