Earlier quoted context omitted.
You don't find out you need to re-register until it's too late.
Don't most places allow same day registration at the polls? Every state I've voted in does. Edit: ok, 2/5ths isn't most but it's still a lot. Chill with the down-votes, it was an honest question, not an attack on your ideology.
> As of June 30, 2019, a total of 21 states plus the District of Columbia have enacted same day registration (SDR), which allows any qualified resident of the state to go to register to vote and cast a ballot all in that day.
http://www.ncsl.org/research/elections-and-campaigns/same-da...
And, same day isn't necessarily the best solution. For example, Oregon does vote-by-mail. This process would make it difficult to allow for same day registration. But, Oregon also has nation leading voter turnout. No polling places, no hassle, just an envelope in the mail.
* Oregon also does automatic registrations when interacting with the DMV.