The two-assembly structure exists because it was a compromise to not give the densely-populated states all the power in the new Republic. Crucially, this sort of compromise was important because it helped the less-populated states get on board with the whole "federal government" concept without fearing that power over their own affairs would be continually swamped by places like New York. "Land" gets voting rights because those who were in charge of that land (the state legislators) wanted it in order to sign onto the project.
This is why I find the modern media complaints trying to do away with such structures very troubling. It may be more vestigial at this point, but the setup was supposed to emphasize a collection of states rather than mere administrative subdivisions of a faraway government. Frankly, if there would be any change to the state-based system for senators, it should come with a free ability for smaller states to secede as a group; because it would be going back on the deal.