Lets take these things one at a time shall we. First of all I must say that I usually believe in anything. Chubakabra, Abdomnimdabohl Snowmen, and things of the sort. But none the less I will try and state my reasons so you can disagree with them.
1) If you think it is odd that this thing has never been found I also consider it odd that no remains of any kind of "missing link" have been found.
2) If you think it is odd because this animal is supposed to be so big that it has not been found I point to the story of the 15 ft tall bear recently killed in Alaska. If you do a quick search you might be able to find this story. Bears were not believed to ever grow as large as this one. But this bear lived many years undetected in the wild. Until it ate 2 hikers and almost ate a park ranger.
3) My third reason for believeing in bigfoot is simple, I don't think that the vast majority of individuals who devote their a significant portion of their time searching are quacks. I have seen interviews with a lot of credible people who claim to have seen/heard or have seen evidence of bigfoot that they can not explain. I have seen a lot more credible people come forward for bigfoot than say "Creationism" which we can agree is not reality. Anyway, my time to type this is short so feel free to let the bigfoot/Brad bashing commence.