How could they not have noticed?

Special Prosecutor Durham has filed new court papers as of this past week and there is much to-do.  For the mainstream media, the position seems to be that there is nothing to be seen.  For some of the more extreme alternate media, the filings are an indication of a collapsing system of government.

As far as I can tell, this is an incremental advance of the case.  It confirms that the Clinton campaign was the source of the Russia collusion allegations, that the Clinton campaign sought to bring these baseless and manufactured charges to the attention of law enforcement such as the FBI, and that senior members of the current administration were part of the Clinton campaign to purvey false information.

What has really interested me has, as far as I can tell, received zero attention.  The actions documented in court filings are that of spying by a private entity on a private entity (the Trump campaign) as well as spying by a private entity on the Trump administration once it had transitioned to the White House.

My question:  How could a private entity (much less a public entity) escape notice of the spying being conducted against the White House.  In movie, story and news report our intelligence services are represented as cutting edge.  How could they not notice the spying that was going on?