Why are there so many death hoaxes?

In short, because people want to read them. For obvious reasons: it would be big news if Clint Eastwood died. The fact that he hasn't doesn't stop people.

It's also a good thing to fake: unlike many other claims, it's not possible to instantly debunk unless you are with the person at that moment. When Sylvester Stallone was the subject of a similar hoax, for instance, it kicked off overnight US time – which meant that he and his representatives were asleep, making it impossible to check whether it was true and so to debunk it.

That's why it took until the evening after it began for Stallone and his brother to get online and confirm that he was still alive.