Developing a drug is an economically difficult thing: Spend billions for the chance to win billions. The only alternatives to big pharma in developing these drugs are big government and big charity (Gates' Foundation et al).
It's only a "priority for evolution" to prevent cancer before the better years for breeding have passed - and evolution has done a fairly good job with that. After breeding and a little time for rearing young in the higher life forms, evolution has no real use for us.
Cancer affecting the old is not strongly de-selected for by evolution.
I also don't subscribe to the theory that individuals have to procreate to boost the survival of their genes. In reality it's a bit more complex than that, and even very old people can and do contribute to the survival of their children or their close relatives.