Because I don't see any reason why it couldn't exist, just that I haven't seen any evidence that proves - for me, personally - that it does exist. I've been fascinated with the big guy since I saw "The Legend of Boggy Creek" at a drive-in when I was 11 years old. I love the mythology, the campfire tales nature of it all. And I'm also fascinated with people who claim to have clear and unencumbered sightings, with no doubt in their minds to what they saw. People who seem earnest and sincere and level-headed. So I pay attention to the subject, refuse to call anyone a liar (while knowing full well people do it all the time - just for kicks even), and maintain the right to expect better evidence.
If the big guy is real, for those of you that have seen one I don't know whether to envy you or feel sorry for you. I think we all, at one time or another, have had the frustrating feeling of knowing you were 100% right on something and have been treated dismissively or laughed at. Sucks, don't it? I have no interest in making fun of anyone or scoffing at them. I have no interest in arguing with anyone - believe me there are a LOT of things I have less belief in than BF, and so have no interest in reading about or arguing over the merits of them. But I do BF, and it's simple as that.
So I will take it seriously, even if I'm not a believer. Like a lot of so-called "fringe" interests, there is a sliding scale of credibility for me. When I see things like the pics of the "Jacob's bear" that certain people are so convinced is a BF when it clearly looks like a mangy bear to me, it makes it harder for me to take the subject seriously. But the sincerity of a lot of you here, and the fact that the PGF still makes the on the back of my neck stand up, keeps me interested.
I've said it before and will continue to say it from the bottom of my heart: I'm rooting for you guys - you BF detectives. I truly am. PROVE it to me.