I would pay normal ticket price at the theater to go to a "movie" that was just 30 or 40 trailers. Like you could have the trailers like normal at the beginning, and then the lights go down and then play like 30 more trailers. I would love that. Or what if they made a trailer that was like 2 hours long, like regular movie length? Would be amazing.

"Nothing but Trailers" on HDNet is pretty close.
Why the hell are they called trailers?
1. They are before the actual movie, they dont trail it.
2. What the frack does a trailer have to do with a movie preview.
Here is your trivia answer for the day...
They used to show 'trailers' at the end of the movie. Obviously people leave as soon as the credits roll so they bumped them to the front. I don't remember how long ago it was, but it way before my time working at Seth Childs, having run the projectors there for many (5) years.
Credits used to be first.
Credits still run first...

You are right though about the credits at the end. I looked it up as I wasn't sure when trailers/credits were used at the front and back.
Looks like trailers moved from the back of the film to the front of the film sometime around the World Wars, probably earlier. Credits have been [mostly] moved to the back since the 70s.
One thing is for sure, after smelling so much popcorn every day for years, I can no longer stand the smell.