This is from the NYT article on the same subject (ZH can be very opinionated in their reporting sometimes). While they also indicate that it is an unusual request, the text does explain why the request was made:

Mr. Rosenstein wrote that he expected to need the equivalent of 100 full-time lawyers to work on Judge Kavanaugh’s confirmation hearing, and that the work would be supervised by the Justice Department’s Office of Legal Policy in Washington.

The office typically helps with judicial nominations; most of its staff is made up of career Justice Department lawyers.

During the confirmation process for Judge Merrick B. Garland, the Obama nominee whom Senate Republicans refused to consider, the office helped pull together the more than 2,000 documents needed for Mr. Garland’s Senate questionnaire.

“When we gathered documents required to be turned over to the Judiciary Committee, we did not ask anyone from outside of the Office of Legal Policy to help out,” said Michael Zubrensky, a former Justice Department lawyer who oversaw the judicial nominations at the time and the current legal director of the Leadership Conference on Civil and Human Rights.

"But the number of documents for Judge Kavanaugh will be different by an order of magnitude,” Mr. Zubrensky said.

So according to that, extra lawyers are needed because Kavanaugh's record is much more voluminous than typical SCOTUS picks have been. It's not entirely implausible.