Probably because there is a lot going on in the center and the bishop is covering the queen. So if bxa3 now black has pinned his knight to his queen and white can push e4 and begin a powerful attack on the center. Dubov would need to use a tempo to greed a pawn that is not part of where the action is in the position.
There's no Doubt ARJUN will be the FUTURE GM#1 coz "KRISHNA always helps his PARTH - ARJUNA" When KRISHNA is on ur SIDE, even the SURYA putra KARAN cant BEAT u , then DOBBY from Harry Potter is just a Wizard GM 😂😂