Given the actual consistent result, it's still probably on the investors for being credulous marks with a case of techno-FOMO and high on their own supply, but I don't think it's always been necessarily so simple on the face of it to be debunked by a bunch of grouchy Internet contrarians in 31 seconds (though probably, again based on the result, was always debunkable by decent independent due-diligence).
After all, it's not hard to imagine a world where SpaceX is a smoking crater in 2015 and we're all going "well obviously you couldn't have landed a rocket, what did they think would happen?!". Another example: the jury's still out on if Uber's long bet on a pivot into self driving taxis can pay off before they bleed out, and you can find plenty of "obviously..." analyses saying they'd be dead or that they'd be the only transport in town by 2020. Neither of those could start in a niche, they were all-or-nothing. And those greenhouses that did start in a niche would have had huge attrition too, again, at the time, each probably seemed like a good plan to invest the family savings into.
It's not unthinkable, to me at least from the outside, that vertical farming had a chance of being a capital-intensive, high-barrier, high-payoff industry. In that I'd be surprised by it about as much as I was by SpaceX's technical payoff about 7 years ago: "huh, so that does work, crazy".
And all that said, if you're an investor who would rather gamble the money than spend a fraction of the promised returns on due diligence, then thanks for the trickle-down, I suppose. And probably just as well farming isn't about to end up in the hands of Farming Uber even faster than it already is becoming.