Was it laziness?
Did they think it wouldn’t make any difference because HRC seemed in the lead?
Did Agent Orange’s hectoring the NY Times have a cumulative effect?
….when we talk about things in the dossier that are confirmed, this is one of the things that I think really stands out as notable, which is that Chris identified Carter Page as someone who had -- seemed to be in the middle of the campaign, between the Trump campaign and the Kremlin, and he later turned out to be an espionage suspect who was, in fact, someone that the FBI had been investigating for years.
Fusion GPS Simpson transcript p.242
It does seem ponderous to read the transcript at 300+ pages, but more interesting is how the GOP cares less about the implications of what even then was apparent Russian involvement and in effect have made themselves enablers of some variety of interference.