Yes, someone can steal your cash - but they can also steal your item.
Setting aside theft - cash is simply the most secure way to ensure you keep your money post-transaction. There is no fraud mechanism to abuse, and no way to reclaim cash once in-hand.
For anything of value, the "old school" rules of meeting in a very public place and only accepting cash are still really sound.
People are still getting scammed with cash every day with fake/locked/misrepresented/stolen items being sold on marketplace sites.
All of the legitimate reasons to reverse a reversible transaction is a fraud vector that cash is vulnerable to. That’s why reversible transactions exist.
100% of the risks you mention are still true with digital transactions. The difference is with cash, you close the door on literal fraudulent transaction claims or stolen accounts. It's vastly safer than digital transactions for in-person sales.
To be blunt - with cash, the buyer can't go home and file an unauthorized/fraud complaint with anyone - the seller has cash-in-hand, is anonymous, and the transaction is non-reversible. That's a benefit for these types of transactions, and one you seem to be overlooking.
If you're selling your couch on Facebook Marketplace - cash is king.
I am disputing your repeated and false claim that there are no fraud vectors with cash.
No payment method prevents fraud.