Basically yes it is that Kn charge home, cavalry try to avoid charging home unless the enemy is disordered - close combat is more decisive.
Some cavalry might therefore often try to evade a Kn charge and get caught, or alternatively stationary cavalry shooters fail to inflict enough damage on Kn charging them, and be relatively easily swept away.
It is also a balancing thing - in DBM Kn had a factor of 4 vs mounted, and cavalry 3. Now that they are both factor 3 the Kn had no advantage in thsi matchup.
Cavalry have some serious advantages in other areas that make up for it - principally vs infantry - plus of course they are cheaper, and irregular Cv(O) is more manouvreable than Irr Kn..