I don't know much about pianos and their actions. Back then, in Mozart's time they used a different type of piano called fortepiano. The actions and hammers were lighter, giving a much lgihter touch, which is also very responsive in good fortepianos. The fortepianos started to be developed during Beethoven's time, developing to the stage of the modern pianos we have here. You must also remember that Mozart used a lot of trills during his day. So prbably you are just a bad triller.
But don't worry I'm in the same boat too. Mastery of trills come with practice and patience.
JL