It is just basic policy on how classified info is handled by the government. The only time automatic declassification happens is when its time window expires (and that can be overridden too). It is usually about 10 years. Otherwise surprisingly it still stays classified even if it leaks all over the internet.

Those who hold a clearance have agreed and signed, under strict penalties, not to process, view, or download classified information on unauthorized machines (their home laptop for instance). In doing so they would be committing a willful security violation -- a serious offence according to the current laws.