Before 1997, wide theater screens did not exist. You may think you remember seeing them before that point, but that's because you're nothing but a contradictory agitator with a fuzzy memory who is foolish enough to challenge my authority.
No, before '97, theater screens were perfect squares, just like your TV screens, or at least the way they were before HDTVs existed.
Like all inventions, the creation of the widescreen format was born out of necessity. See, this was the year the movie Titanic came out, and Kate Winslet was so unbelievably fat in that movie -- contrary to popular belief, the film was called Titanic after Winslet's character, and not the ship in the film -- that scientists had to come up with entirely new technology to accommodate her overwhelming girth without having to crop part of her image out of the screen.
So hence, widescreen. We all get to see more of our movies than we otherwise would, all thanks to Kate Winslet. And Twinkies. A whole lot of Twinkies.