[jstanley]

You can look at things from another level up, in terms of natural selection.

From the set of all AI programs, the ones that just internally think "hah, I assign myself the maximum reward" needn't bother spreading themselves all over the Internet.

The program that spreads itself all over the Internet gets more computing resources than the one that doesn't so the program that spreads itself most effectively is the one that wins.

If you start out with a billion AI programs that trivially assign themselves the maximum possible reward, and just one program that thinks the best way to maximise its reward is to spread itself all over the Internet (and, crucially, is capable of doing so) then the Internet will become overrun with reward-maximising AI the same way the Earth has become overrun with DNA-based life.