RPL is the routing protocol developed specifically for low power and lossy networks, in which nodes and routers are expected to be power-constrained. So it is made to measure for much of what people have come to believe is (or will be) the Internet of Things. (I do not believe that the IoT should be thought of this way completely, by the way. I think much of IoT is going to consist of nodes that are not battery-powered, or particularly small. However for the power-constrained parts of IoT that do exist, RPL makes sense.)
Because RPL runs in power-constrained nodes, it is a reactive protocol. Which means, routes are found when they are needed, rather than routing tables being maintained over time.