Looked at this way, what the Bureau did was so transparently absurd as to be laughable. See her conclusion, one with which I concur:
The moral of the story: It’s a weird way to prevent a bank robbery.You really ought to peruse Attkisson's column, one of 2018's few "must reads." Translation for those too busy to do so: The FBI didn't act to prevent or forestall Russian interference. It appears to have acted to frame Donald Trump and those who ran his campaign.
On the other hand, if the FBI’s real goal — in this fractured fairytale — was to frame the hated owner of the bank and his employees, it all makes sense.
Part of the reason the FBI did so is their reward structure: FBI agents are rewarded for convictions obtained. They're not rewarded for spying prevented, which is speculative as it requires proving a negative. This structure makes them a less-than-ideal choice for our nation's counterintelligence organization.