Filing suit at this level is less bitterness and more asking the courts to weigh in on the legality of the matter. I'm the DNC can stoke bitterness and what not, but outside of the usual ho-hum of politics, these kinds of cases are meant to better define laws that on the face of the law seems to have counter purposes.
the lawsuit takes issue with provisions that require voters who register on the same day to produce additional documentation that other voters registering to vote are not required to produce
Elections are supposed to be "fair" which means that all that participate within them are held to the same standard for voting. Having one set of rules for one group and another set of rules for others requires a really good explanation on why that disparity exists. That you might hear is a burden to prove the State's interest. The State could absolutely have such vested interest in "protection" or whatever, but only a Judge can indicate that it is indeed valid. That's that whole separation of powers thing.
From the article:
These provisions are not justified by any sufficient state interest
And yeah, the State has to show that they are after some lofty goal here that can only rectified by have two different sets of rules. And that, that lofty goal is actually to help the people. So if the justification is "to protect the validity of elections" it obviously begs the question, "have you been having issues with the validity of elections?" If they have been having issues, then yeah, there might be a case for it, but if no, then it's going to be a hard sell to the Judge. It's up to the Judge to dictate that fair thing.
So when we say elections should be "fair", well it's up to the courts to dictate what that word means. And we just recently had a SCOTUS case (Moore v. Harper 2023) indicating that Legislatures can't unilaterally dictate that term no matter how hard one tries to squint at Article I, Section 4, Clause 1 of the US Constitution. I'm pretty sure that NC did this to bring this matter back up to SCOTUS to weigh in on... yet again.
The plaintiffs take issue with the fact that those same-day registrants’ ballots would then be discarded if one verification notice is returned undeliverable. The plaintiffs note that registration applications by other voters cannot be rejected unless there are two undeliverable verification notices, and even then, non-same-day voter-registration applicants have a method to appeal the ruling, which is not the case for same-day registrants.
Again the State may have just cause for these "protections", BUT they have to get those reasons validated by a Judge. The State I'm in had the whole "need ID to vote" thing and the Judge was like "Yeah, that's a good idea, but IDs need to be easy to obtain. If IDs are not easy to obtain, then you're creating more a problem than a solution." And like that, we got cheap non-driver license IDs that a birth certificate and a bill that was mailed to you (or your utility or landlord can sign a form) can get you. Having different sets of rules for something that is supposed to be "fair" has to be carefully balanced with a State's vested interest and sometimes to strike that balance requires a bit more from the State.
So just like Trump had his day in court to challenge elections and what not, the DNC is perfectly fine to ask the court "Hey, I don't think the North Carolina Assembly has properly justified the recently passed election laws." It's one of the things about our system, that's actually nice. Our ability to bring about laws into courts to seek clarification from those who wrote it and hold them to the letter of our laws and the intent of them therein.