Why do you leave the Terrapins/Turtles on their backs if they flip over?

Although some people find it distressing to see terrapins/turtles on their backs it is very important that they are left alone for a short period of time to try and turn themselves over. The reason we leave them is because as a rescue we strive to have their enclosure as close to their natural environment as possible. When in the wild they have no choice but to turn themselves back over as there is nobody around to do it for them. When they are upside down we watch and wait and will only intervene when absolutely necessary. We have previously noted that sometimes other terrapins/turtles will help their friends to flip back over as well.