You know you would have thought all the years and years of "donations" to "cancer research" there would be constant news stories about how we accidentally cured a bunch of ancillary medical problems, and wow its all free to everyone because it was from donations!

Never heard a single story like this

Human Genome Project and everything derived from it. IIRC, that was originally proposed as a cancer research project:

"A Turning Point in Cancer Research: Sequencing the Human Genome" - https://www.science.org/doi/10.1126/science.3945817

Even without that I'm not sure why you think that's a good point — it's very easy to find serendipitous examples in medicine in general, e.g. viragra which was initially a heart treatment, or even thalidomide whose anti-cancer uses were suggested by the very birth defects that made it infamous.

Specifically cancer research finding other things by accident:

"Cancer researchers accidentally discover ‘cure’ for baldness, gray hair" - https://technology.inquirer.net/62453/cancer-researchers-acc...

"Cancer Researchers Accidentally Discover New Nylon Process" - https://www.popularmechanics.com/science/health/a8135/cancer...

Was there any "productionization" of the "cure" for baldness & gray hair, after it was discovered 7 years ago? I reckon, there's a huge market for that cure.

Budgets are finite, and most science funding involves some decision making about how to allocate resources.

And you can't know where to allocate resources best until after the science is done (unless a field/group is known to scam).

It’s a non-profit volunteer run project. People spend more money on stamp collections.

Although for what we know now, we definitely can't understand the territory without a map.

Funding agencies often have to prioritize projects that show potential

Research thrives on curiosity