How did popcorn become synonymous with watching movies?

Popcorn only began being sold in movie theaters successfully in 1912. Then the only way to pop the delectable treat was at home. Like the street vendors, they would have to pop it in a wire cage over an open flame. This was not a very good technique since it had to be delivered to the movie theater and by that time the popcorn was cold. Also the popping method was haphazard at best. The corn was usually dry and most did not pop in a uniformed manner. This also did not go over well the buying public either who could buy it hot off of the streets. Charles Cretors, who invented the first patented steam driven popcorn machine that popped the corn in oil in 1885. Mr. Cretors' machine popped the corn in one-third clarified butter, two-thirds lard and salt. This could stand the 450 degrees which could pop the corn without too much smoke. A fire under a boiler created steam that enabled a small engine to move the gears, shaft and agitator to stir the corn. This also allowed a clown called the Tosty Rosty Man to attract the movie patrons to where the popcorn was. That is, if the smell didn't attract them first!