I used to work in the pharmaceutical industry and my experience is that people in this field in particular are extremely passionate - you can immediately tell who lost loved ones to cancer.
There will always be a reason why people die, and it will never feel like we're doing enough.
The other reason might be, we introduced lots of new cancer inducing compounds.
Also cancer is very complex and a broad term. "Solving" it likely requires solving the human body first, as in understanding every mechanism to the finest details.
Today, most people say "human biology is a thing of wonder" "Humans are built for longevity". And when a terrible ailment strikes, they explain it with "The meaning of life/God/The devil/We must die of something!"
In my mind, we could create a human systems biology profession where students are told during the first day at school "human biology is a mess wrought up by mindless evolution. Your job is to bring it to the exacting standards of perfection that we are able to apply to other things. In the measure we succeed, we will be able to bring dignity to billions of people."
We got some big early wins from low hanging fruit of infant mortality and poor sanitation. Everything else moves the needle a lot less, and it is a really long bug list. Our environment does ongoing damage of many different kinds and we wear out.
Well yes, people will still die, but in the process average life expectancy goes up. I think Aubrey de Grey once said that if you cured cancer and aging then the average life span would be seven hundred years or so, based on death rates due to accidents and murder, etc.
That's the best of humanity: love for fellow human beings, and a desire to preserve life. And seeing that we live in an inconceivably vast and empty universe, I see nothing wrong with the idea.
It's not one disease, it is lots.