A public ledger only ensures that you can see through this if you can verify ownershp of wallets, because as we've seen repeatedly, you can programmatically create an entire eco-system of fake wallets trading back and forth. What's the cost? I can trivially create a series of bots that just trade their coins back and forth with each other forever. It'll create huge volumes. Now the reason you don't do this on real chains is because the transaction costs will cripple you. But transaction costs aren't real if the currency you're paying them in was entirely fictional to start with.
From the outside there is no way of verifying that any chain has any real activity without verifying ownership of the wallets.
Your counterargument here only applies when exchanges participate in the scam. Of course that does happen, and for a long time you could even pay OKeX to do this for you. But it's much less common than obscure coins faking volume off-exchange or faking node activity.
And yet so many instances of crypto coins that did this. I’m pretty sure they all had public books. The challenge isn’t I sell one coin. It’s wash trading. You create sufficient volume from multiple different anonymous accounts continuously. That’s impossible to decipher because ownership is impossible to untangle.
Why does the exchange need to be in on it? If it’s not a KYC exchange, they would have no way of knowing all the Sybil accounts doing the wash trading were being run by the same individual.
Almost all limit order books required posting the assets on the book and take a fee on trades. You can read off the amount paid to generate the fictional market cap and judge for yourself if it's likely to be fake activity. For thinly traded books with low liquidity, it's cheap. For thick books with high volume, it's expensive.
Also exchanges that are not participating in scams, actively or passively, will attempt to detect wash trading and stop it.
It's much easier to fake the initial activity, then start to have "real" users pile on. The only value I created in my ICO was that I created fake demand and the lemmings followed.
From the outside there is no way of verifying that any chain has any real activity without verifying ownership of the wallets.