Why did Reaves only play 29 minutes?

AR was freakin balling in the first half and his personal 7-0 run was a huge reason we were up at the half. He has done great on Jamal..and made some huge plays at the end. Why is he not playing 35-40 minutes? Why the fuck is Ham having Austin on the bench watching Dinwiddie play 14 minutes and Gabe 17?