If it was profitable to test all those, the pharmaceutical companies would be doing so.
It's not profitable to test all of them because it costs so much to run trials, so the companies screen the drugs and choose the ones that have the highest potential for approval combined with the greatest potential for profit. Not a bad model, but it leaves a lot to be desired in my opinion.
For example, let's say a hypothetical potential drug could treat condition x. There are already drugs on the market that treat condition x, but this new drug is potentially 20% more effective and has less side effects. Now, unless the financial projections leaned heavily towards the new drug taking over a significant share of the market a pharm company might not be too excited to invest in trying to get the new drug approved. However, I bet people with condition x sure would appreciate a more effective drug with less side effects.
There is a backlog of untested drugs because of the time and cost it takes to trial and seek approval.
All of this is exactly my point. It doesn't make sense to do so.
So why would investors want to do so, in order to lose money?
In that pool of untested drugs could be an effective treatment for Alzheimer's or something else that would be revolutionary. Why not allow those who are willing to take on the financial risk do so, with the possibility of saving or improving an untold amount of lives, instead of leaving it to the current system of "if we think it will be profitable, then it's worth it".
Because people wouldn't take on that financial risk, which is not a profitable one, as an investment.
Maybe out of altruism. But trying to do it under the guise of capitalism and crowd sourced investments, when it clearly doesn't make sense as an investment is silly.
It's not profitable to do this for the drug companies, or they would do it. So we're going to instead have "investors" throw in money to do the unprofitable trials under the guise that it will suddenly become profitable? Hah, sure.
A better idea would be a nonprofit pharma company that took donations from people to run tests, and took the less promising drugs from big pharma as tax write off donations from them, and did so.
It's still not profitable, but at least we're up front about it and get the same result (potentially discover the cure for XYZ).