Nobody wants willow bark (not totally accurate, but let’s accept it) because aspirin was formulated. That’s not a defense of your argument, it’s the hole in it. Why do you think that mushrooms, unlike willow trees and a thousand other natural sources for what would eventually be synthesized, won’t be made into a superior form by a drug company? Legalizing one opens up opportunities for the latter, which then displaces the old.
Why do you think mushrooms are somehow the exception?
The same mechanics are at work in the current push for cannabis decriminalization and ultimate legalization. It takes the building of a tax base in order to get politicians to take the cause of cannabis seriously. Political economics neatly explain everything about the world we live in.
We already have plenty of regulated drugs which are used recreationally. Adderall, narcotics. You're saying psilocybin isn't special compared to other drugs. You'd be right, except for the fact that there isn't already an industry that exists to cultivate and bring psilocybin mushrooms to people, simply because anyone can go out and pick them themselves. There already was a cannabis industry before legalization, albeit an illegal one. Where is the illegal mushroom business? It's just random people doing it for side profits. Nobody's getting rich off of it.
Because nobody can get rich off of it, there isn't a political economic reason for legalizing it. There might be a public-interest reason, but that means the public has to actually generate more political capital than the anti-drug crowd generates from saying it's horrible in order to get it legalized.
I'm not saying nobody can make money off of psilocybin or that research can't be done. I'm saying that because nobody is already getting rich off of it, its political heft is forever going to be limited to 'mere' public interest.
Cannabis required a public-interest campaign before it could be regulated in one state, because the existing black-market industry had a vested interest in cannabis remaining illegal. Once the regulation enabled taxes, now we're seeing more regulation and legalization.
Cannabis approaches that point where if it were any easier to grow, everyone would. But it's not quite there yet.
Water requires organization but is plentiful enough to be mostly free for typical amounts. Companies that do the organization are heavily regulated and the people running it aren't getting rich.