I got to thinking and.. Sasuke is also receiving a power up from the sage himself. So that means the reason for their power ups is based on the fact they are Indra's and Ashura's transmigrations. So if both receive a huge power up from the sage. The bijuu's giving Naruto their chakra was pointless. He already had the chakra (Ashura's) needed. Sasuke had none of the bijuu's yet he entrusted as well.