The plant is linearized, but the linearization at t=0 is a gain of zero. Most likely this happens due to initial conditions in the model. You can ask the PID Tuner to linearize the model at a simulation snapshot of say t/2, when everything comes to steady state.
When you do that, the PID Tuner successfully linearizes the model and designs a PID controller.
Here are the snapshots of the steps using R2014a.