There's a lot of reasons but the number one one is because there's only a two party system here in the US and the Republican one by it's policies and histories is almost entirely reliant on non-white voters not showing up in the electorate. It's not quiet, in NC they've explicitly targeted voting days and locations that are predominantly Democratic and non-white [0]. Second is just our whole system, the states are independent and run their own voting so tracking movement between states is harder in places that having intentionally done something like motorvotor (where ID and voter registration happen together). [1]
[0] https://www.snopes.com/fact-check/north-carolina-voter-id/
[1] Again generally opposed by Republicans because it would mean more voters which demographically isn't good for them.