Face ID requires confirmation on iPhone and iPad (double click) so on the Mac it would require touching the keyboard or mouse anyway (since you don’t want to accidentally confirm an action by just looking at the dialog box).
Also, when using universal control, my iPad (propped up alongside the Studio Display) will sometime complain my face is too far away for Face ID, so it may be that it’s easier to tune Face ID for handheld devices since the distance from the camera will be more predictable.
Imagine a Face ID Studio Monitor: you’re leaning back in your chair and the Mac says you need to move your face closer, so you then move closer, and now it tells you to double click the mouse or keyboard to confirm. Might as well just put Touch ID on the keyboard to create a more predictable and one-step process.
Also, when using universal control, my iPad (propped up alongside the Studio Display) will sometime complain my face is too far away for Face ID, so it may be that it’s easier to tune Face ID for handheld devices since the distance from the camera will be more predictable.
Imagine a Face ID Studio Monitor: you’re leaning back in your chair and the Mac says you need to move your face closer, so you then move closer, and now it tells you to double click the mouse or keyboard to confirm. Might as well just put Touch ID on the keyboard to create a more predictable and one-step process.