That’s by design. It takes literal seconds to authenticate with Face ID, with just a glance. Double press the button, glance at the screen, ready. Simples.
On older devices, double press the home button while the device is locked to bring up the Apple Pay authentication screen.
Loads of people are still forced to use Oyster, though. I do hope TfL will merge travelcards and contactless cards, and allow discounts to be loaded on contactless cards/accounts eventually. I still use my Oyster card because of the railcard discount I have loaded onto it.