Exactly. This started as an FBI investigation, and instead of cooperating, the FBI and the public quickly discovered that the Trump campaign and surrounding staff were lying to the public, covering facts up, and were willing to commit felonies in order to avoid telling the truth about what was going on.
According R. Trey Gowdy,
lying to the public, while not a crime itself, is evidence of intent and/or consciousness of guilt?
So when the investigators ran into a MOUNTAIN of evidence and/or intent and consciousness of guilt, they pursued it as they should.[1]
Which is typical in a white collar conspiracy. It's why laws like making false statements are so broad, and so critical to law enforcement investigations like this. When the nature of the crimes is just verbal deals between people, there is no smocking gun. You have to actually get people to talk, to reveal what occurred. And if they all decide to lie, the investigation could be prevented from discovering the truth. Investigators can then prosecute them for false statements/obstructing the investigation, in the hopes that they can convince them to cooperate with the investigation. It's as common as it gets. Why are you so bewildered by a professional investigation like this?
The track records indicates more and more people are caught lying and covering up. That's the track record. You do know how many people have been indicted, and convicted, in this investigation I'm sure.
[1] page 215
https://oversight.house.gov/wp-cont...y-interview-transcript-12-7-18_Redacted-1.pdf