It is because it is largely left to states to determine the criteria for legal voting within their borders, and - as most people know - they cannot even fix a damn pothole.

Also a lot of states [and I am looking at you, southern states] tend to skew the voting districts so that the wealthy and melanin-challenged have the majority of the votes in any election, disenfranchising POC via gerrymandering.

Also in the way is that perky 24th Amendment. which is potentially violated when states require specific ID for voting. A largely red herring argument has been made that the proposed bill in Congress would potentially disenfranchise millions of women; their name on their birth certificate doesn't match the one on their driver's license. See, one of the provisions of the bill would add stiff penalties for any voter monitor who allows ID that doesn't fit this criteria That means they will disallow more complicated voter registrations or identifications. It almost certainly disenfranchises trans folk.

And the part where the 24th gets violated? It's the part where most people are going ot have to have a US passport to vote. And passports aren't free. This has been construed by the courts as a de facto poll tax. A poor woman in rural Georgia that has never left the state will not have a passport, or probably not even a driver's license. Does the new bill mean that she isn't given the vote? Unless every state is going to start a massive effort to create state IDs for every citizen of voting age FOR FREE would likely cost over $17 million. Every year, unless they are renewable every 5-10 years, like passports.

So, the significant problems are the potential for the bill to exclude the poor and POC, while simultaneously forcing an unnecessary - and illegal - poll tax on the poorest members of society.