Your ID may not have your correct address, because you recently moved. Heck, I know people who have moved across state borders and gone years without updating their ID.

In that case you can still use it to work, buy alcohol, drive, get government benefits, etc., but you still might need to spend four hours at the DMV in order to use it to vote, because your ballot is customized to your particular city/neighborhood.

So, it's still a tax/restriction which can prevent voter participation.