Not much point in killing a computer you've just unlocked for yourself. Much more profitable to use it as a spam node or launching platform for TCP/UDP/DNS DDOS attacks.

Killing the computer is an easy way to prevent other people from "using it as a spam node or launching platform". I can easily see some misguided gray hat forkbombing exploitable servers to prevent their use by blackhats. Which is why I, too, expected to see the classical bash fork bomb being used in these attacks.

The DoS using "sleep 20", however, sounds like the kind of thing some people consider "harmless fun" (like the many people using LOIC some time ago); it takes the site down, but does no permanent damage and clears itself after a while.