If a device supported and was provisioned with both, and unlocked with either, you would have double the potential for biometric attacks/vulnerabilities (remember that FaceID is an order of magnitude stronger biometric).

If you support just one with the other disabled, it is wasted hardware/space in a device with extremely limited size/cost budget. If you require both, you haven't fixed the usability issues.

Now you're taking up a fair bit of front of the phone real estate (and adding some cost) for a feature that I'm guessing most people don't care about. [ADDED: As others note there are potentially other options though that don't involve putting the home button back.]

My Samsung S10e has the fingerprint reader on the power button. I have it set to recognize my left index finger and right thumb. Works great.

The touchID on my new MacBook Pro is extremely useful. Trained on right index finger.

Fingerprint readers have been living under the screen in other phones for several years now.

How about anywhere cold enough to require gloves, and reasonable enough to require face masks?

In those dire situations I would opt for passcode unlocking with smartphone gloves. Face ID, Touch ID and passcode, only the most extreme scenarios would need more.

That’s great. I’d prefer to use watch unlocking.

Also, these are not “extreme” or “dire” or even uncommon conditions - most of Northern Europe, Canada, and the north-eastern USA experience several months of such conditions every year.

Iris auth on Galaxy S8/S9 was great but it's gone.