Because that is longstanding Department policy?
On the eve of a new administration?
“former State Department official told the Senate Intelligence Committee he destroyed records in January 2017 at the request of former British spy Christopher Steele, according to a report released on Tuesday.”
So, some guy asks a State Department official to destroy State Department records ( purchased/obtained using taxpayers money, this jerk Steel doesn’t work for free) and the said SD official duly obliges! It doesn’t matter the guy was the source of those records, they are still the property of US government.
You just can’t make this stuff up...