They’re official representatives of the NPS, Dept of the Interior and Federal Government. The expectation is that they’ll toe the gubmint line.
Look at it this way, official policy is to deny they’re there. So “Bob Johnson” goes up to “Ranger Smith” and mentions seeing one. Ranger Smith says “Suppose so” and then Bob cites Ranger Smith as validating the sighting (or at least the possbility of one) on his FB page.
Ranger Smith is going to be in a world of hurt for that.
Your explanation makes sense for certain situations and circumstances, but I don't see how acknowledging the possibility that mt. lions may have returned to their former ranges represents a problem for the gov't. There's plenty of food, plenty of space and nothing in the world to prevent them from getting into Ky. A pointless denial just makes them look like the lying clowns they too frequently are.