I don't even know if it's a conscious thing with him. My theory is that he's been living too long in LA and has adopted the fundamental principle of that city: say only what is advantageous for you to say, regardless of what you really believe.
Simmons' road to fame was made in part with a "long-suffering Sox/Pats fan" persona, and also was made by his loyalty to the Celtics, who were never really hated even when they were good. Now that those teams won (and people hate all of them), he occasionally has to cater to that group of readers.
He's like the politician who tacks left/right based on the opponent and the feelings of the voters.