It's more that Everest is the highest peak in the world. If there was another mountain 10m higher than Everest, Everest would get 5-10% of the traffic it currently does.

How many people know the second highest mountain in the world? It's K2, most people have at least heard of it. How about the third highest? Kangchenjunga. Never heard of it, had to Google it.

So for people who want a recognizable achievement, Everest is pretty much the top. Not just in climbing, but any physical achievement. Unless Nepal restricts the number of climbers, it will only get worse.