Well, I don't know that I'd agree that's the only reason. The reason why you might consider the government giving two votes per state regardless of body count is that you can end up in a situation where a party only has to consider the wishes of a fraction of the country when enacting policy. So, in the current situation Mitch McConnell can ignore that the majority of people in this country support things like stricter gun control policies, expanded Medicare, action on Climate Change, easier ballot access etc.
This was less of a problem when filibusters were a thing, because then you would have to court those senators in the middle. Now the GOP can ignore them entirely.