The door sill is OUTSIDE the rubber gasket that makes the door seal. The water you are concerned about is not inside the passenger compartment, it's on the sill. There is a big squishy door gasket between the "dry" area of the car and that water on the sill. Nothing to worry about.
There is lots of water flowing in, around and through many areas on every car.
If you are seeing more on the drivers side compared to the passenger side, this probably means your garage floor is slightly tilted to the left, so more water drips down from the roof onto the left side of the car. Or maybe you make a right turn going into your garage and sling water on the roof across and toward the left side of the car, where it drains down and collects on the sill.
Either way, in rain or car washes, there is a lot of water that flows in the cracks and edges everywhere on every car, as long as it does not leak past the door gaskets, it does not matter. Just wipe it off if it bothers you.
By the way, water around gaskets and sills will dry slower than water on the rest of the exposed surfaces of the car because it does not get as much fresh air circulation.