A lot of it comes down to software. I had a cpu performance scaling bug that meant my oneplus 7 pro would occasionally take ~5 seconds after unlock to stop being clocked at 100mhz. It made the unlock experience really laggy and crappy. It felt cheap and lazy.
But the implementation is often a bit more stable or user friendly. Those features often do not light the world on fire because the user experience is not there yet, and google moves on too fast to finish the feature.