Consider that you can quickly get 30,000 people to sign up for a trial (which is what I saw as the AstroZeneca trial size) but you really have to work to get a sufficient sample size for the right kind of cancer.
Oncology trials can take years. On top of that, teams threw their entire effort into a single vaccine because billions of people will need it, and they may need it multiple times depending on how this vaccine goes. Cancer drugs are often for one type of cancer, which has fewer people and thus less priority.
If 7 billion people were at risk of developing one type of cancer, I think we'd have a better chance at developing it. Cancer is hard but that's not the only reason it's slow.
Oncology trials can take years. On top of that, teams threw their entire effort into a single vaccine because billions of people will need it, and they may need it multiple times depending on how this vaccine goes. Cancer drugs are often for one type of cancer, which has fewer people and thus less priority.
If 7 billion people were at risk of developing one type of cancer, I think we'd have a better chance at developing it. Cancer is hard but that's not the only reason it's slow.