A treatment being approved doesn't mean it's more effective than existing treatments, only that it is effective. And even then, not always as in the case of the controversial Alzheimer's drugs. Looking up some exact numbers on this, for oncology/cancer about 35% of treatments at stage 3 trials will end up approved/produced. [1] This [2] study looked at the 632 medicines approved (in the French market) and found that 25 ended up providing a substantial clinical benefit relative to existing treatments, so a bit under 4%. Even with just those two multipliers you're looking at around a 1% chance of the outcome most people are aiming for with trials.

[1] - https://academic.oup.com/biostatistics/article/20/2/273/4817...

[2] - https://pmc.ncbi.nlm.nih.gov/articles/PMC10660249/