Both of these utilize 3-4 guard lineups a lot.
OKC had SGA and Dort there as forwards alongside Caruso and McCain. San Antonio regularly plays three guards across PG-SG-SF and then plays a wing (Champagnie) or a short chunk combo forward in Keldon Johnson at PF alongside Wemby or Kornet.
Boston typically plays with wings rather than guards. We have only 2 guards in the whole rotation in Pritchard & D White. Then we use the Jays and our young wings J Walsh, Baylor, Hugo. Those young wings do not have the offensive skills to space the floor with three point shooting that those smaller guards have. Nor do they have the ball-handling and secondary passing to attack closeouts. Baylor does have some of those skills. The other two not so much. Hugo shows promise as a passer but was often mistake prone as a rookie. J Walsh rarely shows anything as a ball-handler or passer.
Just ... not a high enough skill level offensively in the role players BOS has on the perimeter.