Diversity? Hahaha.
Americans and Jamaicans are basically a sure thing for short, the Kenyans for long. What are you talking about?
At least in the pool we have the Australians, Yanks, Canadians are emerging, Dutch, Germans, Chinese, Japanese and a few strong swimmers from Britain, France, Sweden and Denmark.
In the last Olympics, 33 different nations won athletics medals (141 total). In the pool, 19 different nations won medals (102 total).
You're probably ignoring the field events. So looking at just the running, on the men's side, 7 sprinting events (400m down) had winners from 5 different countries. And 800m up had winners from 4 different countries over 6 events.
And the women: sprints 4 countries sharing 7 gold medals, and longer stuff had 4 countries (none of which were Kenya) sharing 6 gold medals. If you want to include walks, that's another 3 different countries to add to the mix.
So yeah, when you actually pay attention instead of just relying on outdated stereotypes, you'll find athletics is pretty diverse.
PS I'm not having a crack at you personally, or swimming for that matter, I just hear this sort of thing all the time and I find it annoying.