I realized something else: why would anyone buy 50k in Bitcoin with cash? Exchanges are less risky, and leave a paper trail to explain your spending to taxes. Unless said person doesn't want a paper trail, for instance because it's criminal money. By that logic, it's more likely you'll be dealing with criminals than with honest people, which significantly increases the risk of a cash transaction.
Not necessarily. We have a history here of money exchangers that work only with paper money, even in 2023. Getting paper in money can be more reassuring than getting it in bank (with possible questions asked) and the exchanger knows this.
Actually the fact one gets paper money in hand can make this kind of exchange somewhat safer than on a DEX because the bank may ask about the money from various (maybe very odd) sources your money comes from and you may have no good answers.
Of course, this doesn't mean your use case is impossible. Just it's not the only use case.