I don't think blame is the right term. Yet, there are reasons why this team can't remain consistent in their effort and energy.
With Baynes out again... Horford, at best an undersized center is asked to play out of position. At the age of 33, with a ton of miles on those legs we depend him to compete against younger, hungrier more athletic players. He can't do it anymore, not on a consistent basis. This team needs a healthy Baynes or another true center.
The young players Rozier, Brown, Tatum aren't there yet. Not JUST scoring wise, I'm talking about court awareness, passing, and decision making in general. They'll get there eventually.
IMO some of the problems here come from not knowing when to step forward or when to step aside. (ie the Kyrie effect.) Both players do not play well while being sidekicks. They both don't have the right amount savvy just yet.
Morris is in a FA year. He went from the bench to the starting lineup. God knows who's in his ear, he's now a starter on an NBA team in his FA year. He smells a huge payday.
Haywood has savvy, playmaking, and experience, but his confidence because of the injury is much too fragile. He'll get there.
Kytie sucks all the air out of the room, especially at the games end. Without Kyrie, we have no closer that takes charge. (Marcus Smart wants to but doesn't have the right tools necessary.) The rest of the team are much too used to watching Irving bail them out and take over at the end of the game.
Altogether, it's just not enough.
So here we sit...somewhere between ready to step forward, by trading away the young core for another necessary star FA.
Or, Not signing Kyrie Irving, and waiting for the young players to hopefully mature someday.