Why doesn't UPS/FedEx have Parcel Locker as a delivery option?

I mean there is obviously the default reason being they haven't updated the app yet but parcel lockers have been a thing for a while now. Putting on our PM hat for a second, is there a hidden reason for them not adding it to the app/web as a delivery option? it's all stuff like (front door which could mean front of building or front of apt, back door etc).

Could it just be a liabiity thing? Does delivering it to a locker count as someone having signed for it or not? and if no maybe thats why. Or a time issue. Might add 2-3 mins per delivery.