You have to consider that there are other streams on the same network paths, so simply sending faster doesn't actually mean faster transfers.

It's almost identical to exiting a building during a fire, everyone can rush or exit orderly. Where the bottleneck is the door, and if everyone tries to get through at once, no one will.

Also what's interesting about not going off of packet loss, is that blips in the network are less likely to cause TCP connections to become synchronized and all backoff and re-probe at the same time.