Although thousands of individual cels are required to make an animated film, few cels remain from the classic Disney and Warner Bros. productions of the 1930’s - 1960’s.
The simple fact is that no one believed that the cels and drawings had any artistic, historic, or monetary value. They were making movies, and the artwork was just a means to that end. Once the film was complete, the majority of the artwork was destroyed or discarded and the artists moved on to the next project.
In some cases the cels were washed clean so they could be reused. Many were destroyed for lack of sufficient space to store them. Some were given to children who visited the studios, and often they were encouraged to cut the characters out of the clear background to make them easier to play with. Some were taken home by animators and cel painters, leading to some amazing stories of valuable and historic discoveries in grandma or grandpa’s keepsakes.
It wasn’t until the 1970’s and 80’s that people began to look back at the animated films of the past and begin to recognize the incredible artistry upon which they were built. Sadly, those vintage cels and drawings that survived the years are an extremely small fraction of what once existed.