You pedal to accelerate, but you also pedal to stay at constant speed. Different kinds of friction apply a force backward and you need to apply an equal force forward to stay at constant speed. And friction increases nonlinearly with speed, which is why it's so hard to maintain say 25 mph even on flat ground. You can look up power output for pro racers, and it's very high. As long as you're pedaling at the same cadence, higher power means higher torque (and higher force).