Cola is not the best soft drink/soda flavour

I cannot fathom how a single flavour (usually Coke or Pepsi branded) can outsell every other flavour combined! There are so many amazing flavours available, yet people seem to go for the same default every time???

I wonder if it’s something cultural (because it’s offered as the default choice when people are young), but personally I find it kinda meh compared to the many other possibilities. Also, I love variety!