If it's tap and go, then anyone who steals your card can tap and go all day long. Also, what happens if you tap your wallet and your wallet contains multiple cards with the feature? Can someone brush against you in a crowd and take $20 from your account?
The cards are designed so that if you make a couple of large transactions close to the contactless payment limit they will rapidly fall back to authenticating via chip and pin. It's better then keeping large amounts of cash in your wallet as at least if your wallet is lost or stolen and your contactless card is used fraudulently your bank will refund you.