The issue is that a large percentage of Black/ethnic/poor voters tend to vote Democratic.
As such, from a Republican perspective, the fewer such people vote, overall, the better for them.
One way of doing this is to introduce hurdles that disproportionately affect such voters - such as requiring ID (then making it hard to GET such ID - have a look at getting driving licences in the US, and see where most of the locations you can get them from are located...), preventing people from voting early, such that they have to take time off work (for lower paid workers, very hard to do), making the voting process for those in such area harder, so they are forced to queue for more time etc.
All of the above is a cynical attempt to reduce turnout for Democratic voters, while pretending it is about voter security. They are using the strong belief amongst a number of Republican groups that there was mass fraud in the previous presidential election (there wasn't) as the fig leaf for why they are doing this.