The risks of linking your Uber account to your payment card

A warning to all Uber users. If you link your credit card to your Uber account it is linked to the phone rather than to your cell phone card. If you then give that phone to someone else, the uber account remains with the phone and the new owner can book Uber trips on the phone and it will be charged to your credit card. I recently gave my old phone to my wife and assumed that since I opened my uber account using my cell phone number, that the account would be linked to my cell phone and not my wifes (who of course has her own phone number). The phone was ****** from my wife on a bus trip (in Canada) , and the ***** casually booked Uber trips using the ****** phone which were all charged to my card - not to my wife. By the time my wife had reported the theft and I cancelled my Uber account already a couple of hundred Canadian dollars of fees had been accumulated. Why would Uber not link the payment card details to a cell number rather than to a phone?