I think it’s to create more options.
He’s getting like 7 million anyway.
He’ll be in demand next year with several teams to consider.
Assuming that McCarthy is fired and he would be the backfill may not be a reasonable risk in his situation.
If the goal is to create new options, sitting on the couch while his competition proves it on the field isn't the way. He wasn't as hot a commodity as people expected this year, and has done nothing of note as head coach. I'm not sure why next year would be any different.
He has an opportunity to take a pretty good defensive unit with a few great players, and make them elite. He's a Belichick guy. His system has proven to be effective, with fewer gambles than we saw from Q. If he believes there's a risk to his marketability by taking a high reward opportunity, as an owner, I wouldn't want him as my head coach. Sitting and collecting a check is lazy and ineffective.