" Increasing the minimum data and multicast rate from 1Mbps to 2Mbps "
In wifi networks, you can significantly reduce on-air collisions with other packets if you can send at a higher rate. A packet being sent at 2Mbps spends 1/2 the time on the wireless channel as compared to a one that is sent at 1Mbps. Therefore halving the probability that this packet will collide with some other transmission.