A lot of felines are not very good at high endurance and areobic effort. Some are very fast in short burst like the cheetah. But when it comes to longer activities they will tired faster and is nature way of keeping them alive since swimming will tired then fast and drown.
They're not afraid, they just dont like it. Cats can actually swim. They just can't do it for long periods of time and they definitely dont like to do it.
They Are not AFRAID.. They just dont like getting WET... Dogs and cats can swim..
And I think the change in temperature irritates them.
They don't want to get their furs wet.