There is actually. If you think about it almost every Pokemon with Swift Swim is a water type, meaning that in the rain not only is their speed doubled but their STABs are powered up as well. How would you like having to face a CB Floatzel spamming Waterfall in the rain? You wouldn't, because it is overpowered. Chlorophyll w/ Drought isn't banned because there are no Chlorophyll abusers that have their STAB moves boosted by the sun, and teir fire weaknesses are increased, and since sand doesn't power up any moves (With the exception of Sand Force users), Sand Rush abusers can not have their moved boosted by anything other than an item.