I was suprised by this too. Airlines can override standard MCT for airports, and I have a GDS at work, so I checked there and ET loaded 15 minutes as legal MCT for ET INTL to ET INTL and thus override what the standard MCT is. I suppose they have a valid reason for doing so. Don't know the reason though. Could be anything from
-We will personally pick up guests and bring them to next plane on short connections
-We will have the plane wait
-We will do nothing and have the guest miss their connection and rebook them, as long as we get the booking by offering such short connections


One general questions regarding rebookings though: Ethiopia is yellow fever area. A lot of destinations where ET flies and connects too (i.e. South Africa, but also Zimbabwe) clearly say that any guest who have transited in Ethiopia more than 12 hours needs a yellow fever vaccination certification.
This means that a guest that books Ethiopian i.e. Frankfurt-Addis-Johannesburg on a regular connection with let's say 2 hours layover will be fine. But if the connection is missed or the second leg cancelled at short notice etc it will not be acceptable for ET to rebook to next days flight as this would result in a layover more than 12 hours and consequently denied entry in South Africa. Wouldn't that be a good reason for a passenger to stress ET to be rebooked on another carrier?

It's really quite an issue to have a hub in a yellow fever country. ET i.e. also flies to Botswana and Botswana as per their rules (not sure if they are enforced though) is not accepting passengers that have transited in Ethiopia, even if they remained airside and were there just a single minute.