The statute says that Individualized removals may still occur during the 90-day period because it will lead to a smaller chance for mistakes. However: "For programs that systematically remove voters . . . , Congress decided to be more cautious. At most times during the election cycle, the benefits of systematic programs outweigh the costs because eligible voters who are incorrectly removed have enough time to rectify any errors. In the final days before an election, however, the calculus changes. Eligible voters removed days or weeks before Election Day will likely not be able to correct the State’s errors in time to vote. This is why the 90 Day Provision strikes a careful balance: It permits systematic removal programs at any time except for the 90 days before an election because that is when the risk of disenfranchising eligible voters is the greatest."
That's the Congressional rationale. And it is not to maximize the chances of voter fraud, but rather to minimize the chances of disenfranchising legitimate voters.
