Designed on purpose like that by the Founding Fathers so that smaller states would not be completely overpowered by the states with larger population. Meanwhile providing that in the House of Representatives the representation more reflects population. The two houses (or chambers) of Congress then have to work together to enact legislation (the Senate is often referred to as a "house" when referred to in that context).
It’s not really accurate to say that the system was designed that way by the Founding Fathers. Hamilton, Madison, and Washington, to name some notable examples, hated the idea, but gave in (in the “Great Compromise”) to the reality that the small states would have withdrawn from the Constitutional Convention if they didn’t get their way. Here’s Hamilton on the general subject before he capitulated:
“Every idea of proportion and every rule of fair representation conspire to condemn a principle, which gives to Rhode Island an equal weight in the scale of power with Massachusetts, or Connecticut, or New York; and to Delaware an equal voice in the national deliberations with Pennsylvania, or Virginia, or North Carolina. Its operation contradicts the fundamental maxim of republican government, which requires that the sense of the majority should prevail. Sophistry may reply, that sovereigns are equal, and that a majority of the votes of the States will be a majority of confederated America. But this kind of logical legerdemain will never counteract the plain suggestions of justice and common-sense. It may happen that this majority of States is a small minority of the people of America; and two thirds of the people of America could not long be persuaded, upon the credit of artificial distinctions and syllogistic subtleties, to submit their interests to the management and disposal of one third.”
I don’t think even Lin-Manuel Miranda could set that to music, but it still sounds right to me.
Sorry for the digression; back to obsessing about our Claritys!