Explain Like I'm 5 (ELI5)

Because voting regulations are left to the State governments, and each state government does it slightly differently, often with designs that are specifically intended to disenfranchise specific voters.

Further, because of the Electoral College, it is very important WHERE you vote. If I live in New York, I can't vote in Pennsylvania. I get lumped together with everyone in New York.

So my registration ties me to a "permanent address" that aligns with a state, their electoral college contribution, and the rules they've put in place to gather, validate, and verify the vote, all mixed with manipulation over the years to swing the vote wherever possible (see: gerrymandering)

Different system, no central registration. Just look at the lack of a standardized ID.

It's 1840 over there in that regard.

There is no central id system in the US. There are several things that are close to a national id, like social security numbers, but they are also explicitly not allowed to be used as an id. There's a very long history of US citizens opposing the creation of any sort of national registry.

States have id systems, but they still require a person to manually register for them. There's limited interaction between states, so it's possible to appear as a citizen of two states simultaneously, this is solved with eventual consistency and fraud charges for those who abuse it.

It's getting better in some states, where they can update your voting registration when you change your address. Voting rolls are managed at the city and township level where they generally don't have the resources to properly integrate data, which leads to outdated lists where a one bedroom apartment may have 10 different voters registered that lived there at one point. There's no great way of knowing who the legitimate voters are, and who should be purged as they are no longer eligible to vote there.

There is a need to do some cleaning of the voter rolls, as accurate ones make planning easier. Printing a ballot for each name is wasteful if you know 20% of the names aren't valid, but running out of ballots is unacceptable. Purging people who haven't voted in say 20 years can reduce the number of bad names, but it will almost definitely affect a few people that haven't moved and haven't voted in 20 years. The attack on democracy is more theoretical than practical, that a person is going to suddenly start voting after not doing it for so long.

Every time I go to the states I feel like I'm in a developing country. I've been I places in Africa that feel more like a developed country.

Are they stupid?

Yup!

They keep doing things as if electoral results needed to be delivered via horseback so...

Lot of dumb comments here. Everyone in a country with voting registers to vote, you just may not realize it. In order to vote in an election, the government needs to know that 1) you are a citizen, 2) you are alive, and 3) where you live so they know you can vote in that local district.

Ask yourself, if you moved across your country, how would you vote in those local elections? The answer is that you would register to vote there. You may not see it that way, cause that "registration" may be dual purposed with some other act (like getting a new drivers license), but you are letting the government know you can vote there. Most places in the US (at least everywhere I've lived, I think) allowed me to register to vote when I got my new ID.

The thing that makes it a little different in the US is that registering to vote isn't strictly tied to anything else. If you move from one city to another within the same state, or if you choose not to get a new drivers license in a new state, the government will have no clue where you live. You aren't required to give the government that information. The only time you have to give the government an address is to file taxes (maybe not even then). That doesn't occur until spring, so if you move in the summer, there's no way for the government to know that you can vote in a different place if you don't tell them.