It's easier to say and criticize than to be in the actual situation though. That might be one of the lapses from the coaching staff.
These guys are professional but sometimes there are really times that they can't make a quick decision, not because they didn't think of it but actually they have another thing in mind.
Mav's primary plan is not to foul as they already had a 1 position lead. That's either an overtime or a win. I bet nobody thinks of fouling a Laker and use the foul to give in the first place. That situation was quick and It's already late for them to react as the ball was on Lebron's hand leaving his defender. The help defense from the Mavs to defend Lebron while driving the lane in the dying seconds is somehow unnecessary. Lebron will never take that shot knowing they need 3 to tie the game.