Because, like AI, molecular biology is complicated and there are no quick hacks . Some things are meant to take time and be right. First time. Survival rates are spectacularly better than they were fifteen or twenty years ago and they are getting better all the time. Also there is no one type of lung cancer, brain tumour or bladder or bowel cancer either. There are many different types. Half the battle is identifying…
This is a kind of cool Wiki article: http://en.wikipedia.org/wiki/History_of_molecular_biology
But the discipline isn't even 100 years old yet, and really only in the last couple of decades have we been able to have technology to really take advantage of isolation. We have learned so much about modern medicine, but have so much more to go.