Not a surprise. One of the Sox hard-and-fast rules seems to be "don't ever have a manager in the final year of his contract" - the constant media attention to the "will he or won't he come back?" saga isn't worth the hassle. They obviously weren't going to fire him going into 2022, so they needed to extend him. Besides, manager contracts are the only contracts in baseball that don't cost anything other than money, so there's not much downside in using contract length to show support for the manager.