Any barrier will knock people out of voting. Seth says 218,000 may be blocked from voting. Each set of the way knocks more people out.
Everyone must know about the law. A lot of people may not follow the news, or have access to it in their language. It's up to the state and towns to get the word out. So they have to reach people online, in newsletters, print out pamphlets, have them available in multiple languages, etc. Trust me, state and local offices are already over-busy without that. Maybe that means 50,000 people will show on on election day with no clue about this new law.
Even if people heard about it, it means a trip to the DMV. Some people might just put it off until it's too late, some people might not have an easy way to get there, like the elderly, some may not have a weekday to get there, some DMVs are only open certain days of the week or even certain days of the month. There's also single parents (generally single mothers) who don't have time to wait in the DMV for hours with their young kid. For them, 2 hours is just too much. Plus women who have had their named changed like in the video so boom you have disenfranchised a lot of women specifically. So maybe 100,000 just don't take this extra step.
They need to know which documentation they need and have that documentation. Again with having to get specific information out. Some people may have lost this documentation over their lives. Like in the video, a woman presented 5 different pieces of ID but was denied. so that's probably another 50,000 people.
It costs money to get an ID. Even if it's 10$, a lot of people don't have any extra cash. And with each dollar increase that's another person who looks at that and says "I just can't afford that this month." That's another 18,000 people.