When you have cash, it's difficult to stop you from spending it as long as someone is willing to accept it as payment. You have direct access to your cash and how it's spent.

When you have money in a bank account or the layers that live above it like PayPal or Venmo, you can spend your money only with the permission of the bank, PayPal or Venmo. Your payments and access to your money can be stopped.

When you have bitcoin, you get back to a cash-like system where no one can stop you from accessing or spending YOUR money.