Why can't online purchases be as easy as point-of-sale purchases?

I recently lost my wallet, and while I wait for new cards to come, I'm completely dependant on my phone's tap-to-pay for goods. (It's awesome that my primary credit card could update my Google wallet with the new card electronically!)

It occurred to me though, that in person, proximity of my phone to the card reader automatically submits a payment, even though, on the exact same phone, I can't use the browser to do the same thing. Yes, the phone os can fill in my card numbers, but I still need to put in my card security code, which I don't have at the moment. Those numbers are laughably small anyway, usually 3 or 4 digits in length. Why is my phone so trusted in person and untrusted over the Internet, when though, really, both times the payment is being processed over the Internet.