These guys (KG, PP, Ray, Rondo, JO) are veteran players. They've been coached by great coaches. Do the REALLY need another guy telling them what to do? Did they just forget everything they've been taught?
No... The problem is not coaching...it's called age, declining skills, offseason laziness (to a degree), and maybe a bit of "we'll just show up and run the table" overconfidence.
The new guys? The younger guys? There's enough veteran leadership for them to fall into line. (And it's not like the new guys don't know the system the Celtics play, especially Bass as he's played numerous games against the Celtics and would be very familiar with the system).