Why does a rocket with more mass need more thrust to launch it?

The reason why this is needed is because a rocket with more mass is going to speed up slower. This happens due to the rocket being up in the air, and the force of gravity is now acting in the opposite direction of thrust, so now the amount of thrust that is pushing the rocket upwards is decreased. As well as that, you now have to increase the amount of upwards thrust to counteract this. For Example, the Saturn V rocket engine.