An increase in the demand for bubble gum might be caused by

An increase in the demand for bubble gum might be caused: by the fact that blowing bubbles is now a popular activity

In marketing, bubble gum is considered as an Unsought product, which is a type of product that wouldn't be bought by customers under normal conditions. This type of products usually had a really high demand when it still becomes a trend and will dramatically decrease as soon as the trend faded out.