It happens slowly, when you aren't looking.
You buy a 2nd refrigerator for the garage and have to move your tool storage around.
Now your bicycles have no where to be, so they are right up against the car.
Then, you get a little baseball equipment. Not much, but its easier to keep here at the house instead of taking it up to the field.
And maybe your microwave dies and you get a new one - and put the old one in the garage.
And maybe a few folding chairs, winter boots, deflated balls, roller skates, sidewalk chalk, moon sand, jump ropes, and other kids toys don't always make their way back to their storage place.
And before you know it, you only have room for 1 car! The other is in the driveway.
And to every single one of you laughing right now, I know who you are! :)