Not so odd historically; the enactment of disenfranchisement for all felonies (as opposed to particularly major or election-related ones) started in the South as part of the Jim Crow policies to disenfranchise Black voters. Together with the use of the criminal justice system to disproportionately target Black people, this allowed starts to disenfranchise those voters without an explicit racial reference in the law.
It's odd that the USA, which champions democracy, doesn't hold the right to vote as a universal and inalienable right of all citizens.