It isn’t. The Republicans have seen that the more people that vote, the more elections they lose. A healthy political party would use this fact to reexamine their views and the policies they support/oppose. (For example, reduce the anti-abortion and anti-LGBTQ rhetoric and focus on budgetary conservatism.
The Republican party isn’t a healthy political party, though. So instead of changing to reflect what the voters want, they are trying to change the voters. Since they can’t force voters to support what they (the Republicans) want, the Republicans are trying to change WHO is a voter.
If you support what they want, then congratulations. You’re a legitimate voter. If you oppose them, then you’ll be stripped from the voting rolls and will have roadblocks erected to prevent you from getting your voting rights back.