Back in the day there was only Red Bull and Battery, but they were expensive as fuck, so most kids didn't want to waste their pocket money on them. A few label brands emerged soon but they tasted like shit in comparison. Then ES came and it tasted like normal energy drink and a 0,5l can cost only 1€ so it was cheaper than coca cola or any other conventional soft drink. So obviously all the kids started drinking it. It was both cheap and a novelty at the time.