The thing you never acknowledge is that it's not that simple. Our Federal system takes not only raw population into account, but also the fact that the *distribution* of the population hugely affects how people vote.
Once you take that key ethos away from the Presidency, how long until we start hearing, "bUt cOnGrEsS iSn'T dEmOcRaTiC" because the Senate, which EXCLUSIVELY represents equal states and yet often controls key aspects of Congress, is sticking up for the Wyoming's, Alaska's, and West Virginia's of our nation?
The Legislative and Executive branch are determined via a process that balances population with distribution EXTREMELY well. Don't like it? Nominate candidates who are better at attracting the attention of more Americans across different geopolitical groupings.
For the record...you Democrats missed a HUGE opportunity with Steve Bullock in the 2019 nominations. He was massively popular here in red Montana and would have been better at Biden's, "moderate, grounded American" schtick than Biden is himself.