That’s not really fair. A good number of people provided them with sound advice. A few people advised them to report it to Monzo:
You yourself then echo this advice in your opening post:
The issue was, the OP in the other thread you reference was insisting on reuniting it with the owner via unconventional means, and people tried to adapt their advice to suit. That user quite clearly wasn’t open to any suggestion other than finding a way to put them in contact with the wallet (containing a significant amount of cash) owner directly.
Noting that it’s a wallet containing cash here is quite important, because it brings us to the resource I shared earlier:
This means the police would have accepted the wallet and processed it accordingly. So the other advice they received from a good number of other folks to hand the wallet into the police is also acceptable.
As is evident here, a lot of people tried to help, and offered objectively good advice and provided the correct etiquette to follow. Even your own personal advice shared in this thread was provided to that user in their thread already.
People helped. And they’re not all of a sudden experts now. I presume they merely read what you posted and decided to check with their local constabulary from the looks of things, like I did for Scotland.