I am learning about the roman empire and am thoroughly enjoying it but as I was reading about how popular the gladiator contests were, I wondered why it has stopped being practiced but the Olympics have become a worldwide event
The Olympics as we know it started in 1894 (with the first games being held in 1896) when the IOC was created by Baron Pierre de Coubertin^ref. Before that there were a few tries in the late 17th to mid-19th centuries to start something, but nothing really stuck, and they were mostly attended by entrants from one region of a single country.^ref
It's also worth noting that the ancient games were not just sports, and had events for sculpting, poetry, painting, etc.^ref
So, there's 1400-1500 years without Olympics and the ones before that gap were quite different to the ones we have now. It's more a case of 'inspired by' than the original thing lasting and growing.
Gladiator fights to the death haven't stuck around, but combat sports such as boxing, wrestling, martial arts, fencing, etc. have basically always been popular.