It turns out Bolton's home was raided because during Biden's presidency intelligence officials stole information from a foreign adversary's spy agency which contained emails sent by John Bolton containing classified information. They were sent over unclassified email, and he was leaking the information to write his book.
https://www.nytimes.com/2025/08/27/us/politics/bolton-trump-emails-fbi-investigation.html
John Bolton Inquiry Eyes Emails Obtained by Foreign Government
It is not clear what country intercepted Mr. Bolton’s private emails, but the investigation into President Trump’s former national security adviser picked up momentum under the Biden administration.

The investigation into President Trump’s former national security adviser, John R. Bolton, began to pick up momentum during the Biden administration, when U.S. intelligence officials collected information that appeared to show that he had mishandled classified information, according to people familiar with the inquiry.
The United States gathered data from an adversarial country’s spy service, including emails with sensitive information that Mr. Bolton, while still working in the first Trump administration, appeared to have sent to people close to him on an unclassified system, the people said, speaking on the condition of anonymity to discuss a sensitive case that remains open.
The investigation of Mr. Bolton, who has become an ardent critic of the president, burst back into public view last week when federal agents searched his Maryland home and Washington office.