The price elasticity of demand (i.e., the amount someone changes purchasing decisions based on price changes) depend in part on how much of your budget the item takes up. For wealthy people, soda is a rounding error on a rounding error. For lower income folks, soda could be a small but noticeable percentage of their budget. So 20¢ is not 20¢ to everyone.

For my part, I know that teenager-me would have absolutely noticed this price increase, but adult me would not.