The US has had a long history of restricting who gets to vote. Originally it was only white land owning males, then it has gradually progressed into what it is today. Some states are cool with who gets to vote, others are still upset there are certain groups of people who get to vote who they wish didn’t (and actively work towards restricting or removing their rights), so those upset states constantly create as many barriers as possible to disenfranchise groups of voters they don’t like. If you’d like to see how awful it has been before, I suggest reading about Jim Crow laws.