We don’t know that for a fact at all...
“As long as Mr. Brown is a free agent, placement on the Commissioner’s exempt list is not appropriate. If he is signed by a club, such placement may become appropriate at any time depending on the status of the investigation. Upon the conclusion of the investigation, he may also be subject to discipline if the investigation finds that he has violated the law or league policies.”
You’ve already signed him at this point, and the NFL didn’t put Hill on the exempt list, so you keep him and force their hand. If they do, you part ways then. The Patriots didn’t wait for that because the old yenta, Kraft, decided to stick his nose into the football operations side. The side that’s supposed to be Belichick’s business. He did that because his little rub and tug situation kept coming up and, considering his hard line stances on women, he couldn’t have that. It was, and has been, a massive hit to the offensive side of the ball that hopefully Sanu and Harry can mitigate eventually.