Who was the ace of the World Series champion that season?
The Sox tried the "groundball pitcher" approach, with guys like Porcello, Miley, and Masterson all having history if inducing lots of groundballs. And Sandoval actually had a solid history as a defensive 3B, giving them what should have been a good defensive infield. There was a strategy in place here. They even moved their worst defensive infielder to the outfield, possibly hoping the high groundball totals would mask his deficiencies.
They were not helped by a lot of people having flat out bad seasons, highlighted by Masterson, who was roughly a 4 fWAR pitcher for the Guardians, but a negative fWAR pitcher upon returning to Boston despite still only being 30 years old. And also by Sandoval and Ramirez, who at times looked like neither had ever played baseball before...
And don't forget, the Sox had some sort of moratorium on giving out big contracts to pitchers over 30. That's a deathnail on the free agent market, where the overwhelming bulk of pitchers are at least 30 years old...