Yup. This is clearly so. If they exist, their numbers are extremely low.
Actually, you can hit it without ever seeing it, especially at night, which is the most likely time one would be hit. And yes, most large animals (larger than deer) get hit and make it iff the road to die nearby ir even quite a ways off. But I've seen lots of moose over 1000 lbs get hit and die right there on the road. This, too, attests to the low numbers or nonexistence of these animals.
Wildlife biologists, primarily employed by state fish and game agencies, but also by feds overseeing federal classified lands like wildlife refuges. Obviously, due to the low nipumber of these creatures and their selective habitat, not all biologists would know. Just those who happened to come across evidence and those upper level people they quietly reported it to.
First, because the stigma of denial surrounding the nature of the myth, then after considering the ramifications of discovery, the wisdom of realizing that the best course is silence. That second factor might be laid out to them after consultation with upper management. As a former government official, I can attest that the initial reaction to any knowledge whatsoever was silence after handing it off to my superiors, and from there the "need to know" ruled.
Institutional behavior. Everybody just knows or perceives. If somebody breaks the protocol (which we see with reports from former or anonymous employees), official denial or ignoring makes said violation just another unconfirmed report.
Killing Gimlin would be more dangerous than productive. Obviously, the practice of official silence has worked for half a century with the film. But that film event was key in official experience. I believe they realized that such an event must be discouraged from happening again. Since the PG filming, the access restrictions, commercial filming permitting rules, and other tightly controlled land and visitor management policies that they love so dearly have helped them prevent another such discovery opportunity.
Passive discrediting and keeping the phenomenon a myth is the better approach than offensively disappearing people and programs. They cannot and never will completely eliminate the phenomenon. It has lived longer than even government has. It has followed our species throughout time. But keeping it in the realm of other myths? Much easier, especially since the species is going extinct, anyways. A thousand years from now, they'll come out with fossils and tell people that another species of human was killed off by our own, and that justifies population control.