This sounds like the same reasoning that Horford used. He is not going to get more per year than the current $25M but he probably can get 3 years at maybe $18? Plus he gets out of SAC if he wants to. I think it is actually less risk than playing out the final year and risking injury or performance decline.
You can come up with good or bad examples but do you think IT is wishing he had extended somehow over playing out his contract? Sure, if you play great and are healthy, you can max $$ but Barnes can also lock up say $50M-$60M or maybe more, guaranteed, just like Horford.