Besides a brand with a huge history, in some situations, cola can really be useful. Phosphoric acid, which is contained in cola, helps with hangovers, toxicosis and nausea.
Benefit and popularity are not related in this case.
With some caveat, the readiness of the energy contained in cola in the form of sugar can be called with some caveat, and also a good mood from drinking a cool drink on a hot day.
I read on Wikipedia that in Hong Kong hot cola is used as a cure for colds.
The popularity, I think, lies in the popularity of the brand and its long history. The company has existed for over 130 years (it was founded in 1886) and managed to gain a foothold as a major sponsor, organizer and partner of many international events, for example, the Olympic Games.