This is called paying them, and occurs even in the absense of tips. Tips give people the second option of not subsidizing the corporation; were tips removed, everyone would be forced to subsidize equally. This is to the business' disadvantage only because some people are willing to pay more when it is in the form of a tip then the corporation could ask the rest of their market to pay.
You think of Uber as the employer, and yourself as a mere customer, but it is just as apt to think of yourself as the employer and the driver as your employee. If we do so, the money Uber gives the driver, as well as any tips you provide, become the employee's wage. From here we see you are paying them an unlivable wage, and should be scolded the same as any employer doing the same.