JB had him covered.
You can see in that screenshot you posted that Ant's left leg is completely extended out and he wouldn't have generated enough upward force to jump off that step. Which is further emphasized by him having to arc towards the basket because JB is bodying him away from the paint, making it harder to generate force to leap because you're overcompensating by taking either longer or awkward strides to balance yourself to correct your path to the rim.
He would've had to take another step to jump, which if you see his very next step in the next frame -
His next step leaves him directly under the basket and JB has already taken off anticipating a shot.
The only possible way that would've resulted in points is him getting fouled, and with the T'Wolves being away from home and on the last possession, the refs would've had to see him get killed to make that call. The very fact he didn't even try to jump should tell us that he wasn't in a position to; it's not like he's p*ssy and passes up shots in those situations all the time, or is scared of taking it to the hole.
Given the Celtics were willing not to double him, and JB was riding his hip from the top, it wouldn't have taken much to drift hard left and then snatch right back towards the middle of the floor, where he would've had just under four seconds to create a good look.