Mainly because for just about every aircraft in this thread, it is 'guessed' within one or two posts or the picture being put up. For some planes that's to be expected. Most people (including myself) could identify a C150 from a mile off.
However, there are so many rare planes in here that there's no chance people are just getting them off the top of their heads. There'll be a picture of an obscure amphibian plane that only flew 7 times in 1964 and someone will apparently know the cockpit layout. I don't think so.
Not that I'm attacking the integrity of anyone in here, it's only an informal game, but there are definately some porkies being told.