I think the question was more about „Why do i have to register to be able to vote?“
Which is a good question. In germany we don‘t have to register to vote at any level. Once we‘re 18 and are registered citizens (the latter part is indeed a problem for immigrants due to bureaucracy), we get to vote.
We get a letter informing us where our local poll station is and then go there. A poll helper then crosses our names off a list once we‘re there and our ID is validated. Or we use the included ballot and send the letter back for mail-in voting. We can also have someone else vote for us if, say, the accessibility measures at the local poll station still don‘t suffice.
Germany isn‘t a perfect state but i personally think they make damn sure that you can vote. And it‘s really problematic that the ostensibly democratic US doesn‘t nearly put as much effort into enabling people to vote.