I believe the Red Sox FO, at their annual season-ending press conference after 2018, were talking about the future of the team and they said while they'd love to be able to keep all of Betts, Bogaerts and Sale, they didn't think they'd be able to keep all of them.
I think they went to Mookie first, and based on his counter-offer they decided he was simply determined to go to free agency. This was in keeping with all Mookie's words and actions on the matter.
Then they went to Sale and Bogaerts and got those extensions done.
Seems perfectly simple and logical to me.