It’s very hard to find remains of animals. Sure you find some every now and then. When was the last time someone found the remains from a bear or lynx? Not often.
Rodents love to chew up of bones and our vultures, the bird type, not the lawyers do a great job of cleaning up.
Red eyes? Mothman lives.
It's been a while, but I've seen a black bear that was road kill on the highway before.
While I haven't seen the remains of many such animals personally, it isn't that uncommon to find remains in their natural habitats, and while there are far more bears, we aren't talking about something being rare, we're talking about them never being found.
They are saying that there are 3500 currently living nationwide. However, since some die and others are born over time, we are talking about more than a few thousand, and we are talking about remains that would be very unusual and would be far more likely to get reported than something like bear remains.
Sure scavengers will destroy some remains given time, but having never found remains? Not even close to being credible.