Cancer is simply cells breaking free of the cooperative jail. Essentially the grey goo scenario of nano machines. Instead of cooperation they just do their own thing.

Cells have a certain optimised DNA mutation rate kept in check by various machinery. Multi cellular life expects each of these little replication machine to co-operate in the grand scheme of running a body. But it's also required in the grand scheme for DNA to mutate a little bit to ensure population variance. So you could say that cancer is the tax paid for having cooperative yet flexible and adaptive nano machinery.

So yes the propensity for cancer developed under evolutioniary pressure towards a non zero level.

The population could have optimised for zero cancer but it would not have paid for itself in terms of overall population adaptability and survival.

You can see possible existing environments even if you explicitly blind yourself to them, through reflections off of environments that you do not blind yourself to. Even with the benchmark excluded, the social zeitgeist that has considered the benchmark and included it or ideas from the benchmark either implicitly or explicitly in their code, documentation, et cetera is still part of your training data.

Because then you could sit under the palm tree and enjoy your free bananas and relax.

Propagation