I blame Ainge and Stevens, not the players. Ainge, in my view deserves the brunt of the blame for doing nothing at the trade deadline to improve rebounding and defense up front. Which he could have done without endangering his precious cap space this summer. There were people available who could be had for secondary draft picks and players.
Stevens may have to share some of this blame, too, since he apparently has an equal say with Wyc on player personal, and seems to abhor any big man who can't shoot the 3 and may take away from the offense (AJ comes to mind). The conflicting quotes of Danny "Our biggest need is a rim protector" and "Rebounding detracts from offense" are a sign of possible discord.
And further, what the players think about all this--which may have affected their morale coming into the playoffs. They perhaps know the team flaws better than anybody.