The desire for attention is motive enough.
Just curious, but these people who told you about their encounters... what was the context? Why did they talk to you about that subject in particular, rather than their kid's soccer team or the weather or whatnot?
I agree Kilaak that some people crave enough attention that they'll say anything to be the center of attention (excellent question btw). But I can't say with any certainty that claims of such nature are driven by this, or anything for that matter.
First account - My mining partner and I currently have a claim in the Pacific NW, pretty far out in the sticks as well. He had been doing this for a while back in the 80's and 90's and for circumstances out of his control, had to take a break. When we were planning for our first exploration in this new area, we were discussing needed defense when we were out in the backcountry as humans aren't necessarily on the top of the food chain in the wild. The whole conversation started with "I don't want you to think I'm crazy, but there's something else we may have to contend with......"
Second account - During my second exploration in the area, we were taking an evening off for some decent food and libations, we got a space at a local campground. After meeting the 'neighbors', conversation around the campfire turned to the woods, and the legend of BF in the area. After a few minutes of discussion, one of the 'neighbors' offered an account they experienced of seeing a large ape-like creature running across a field on 2 legs - faster than seemed real at the time, cross the road in front of them, him and the passengers of the car were basically besides themselves as to what they had just seen. When they approached the area where the thing crossed the road, they experienced the "BF Stench" so many eye-witnesses describe.
Third account - My gf works in the newspaper business, when doing a story on an Indian Reservation, she spoke with a tribal leader and noticed a map on the wall with a bunch of marks on it. This leader kept a map of all of the sightings on the reservation for 20+ years. She mentioned this back at her workplace and one of the older ladies (50+) came into her office and told her of a story of her and her daughter driving down a mountain road in a snow storm - going about 20 mph and seeing a large black creature cross the road in front of them walking upright, it stopped in the ditch to look back at the vehicle. They stopped the car and observed it for several seconds before it went back in the brush. They looked at each other and basically realized that no one would believe what they saw, and continued driving.
Fourth account - A friend of mine spent 8 years in the Pacific NW (Northern CA) & had a small vegetable farm in the hills. One summer night he heard what he thought were the lions screaming in the hills, but something didn't sound right, he went outside and could hear several places where screams, whoops, and loud banging were coming from the woods around his place. He said in a split second it all stopped, then an earthquake hit.
Now, of course I've no evidence of anything, and am not speculating that these incidents are indeed a BF, but my point here is not to prove any of these encounters actually happened, but merely saying that I, personally, find it peculiar that these seemingly well-rounded folks would make up stories of such a nature for attention.
Again I'll bring up the difference between possibility and probability and can anyone definitely say the probability is zero.
I don't think the nay-sayers will EVER be able to prove, without a doubt, that BF (large NA primate) doesn't exist. The burden is on the believers, with only 1 solution to the arguement - find, document, and provide a BF to the public. Until then, the romance of the potential will always be there, makes for some interesting discussions and internet searching to say the least.
Thx