Is there a reason Bards and Druids get so little new crunch?

@PandaemoniUnearthed Arc, SCAG, DMG and Elem Evil guides, is there a reason Bards and Druids get so little new crunch? #bardicinspiration haven't seen big demand for it – think PHB hits biggest archetypes. That said, might have some bard stuff soon in UA.

— Mike Mearls (@mikemearls) December 16, 2015