Not "inherently" a problem, but it doesn't really fit what the league wants. A scrum for a loose ball is more exciting than a ball casually wacked out of bounds, especially if it could lead to a touchdown.
Anywhere else on the field, a ball fumbled out of bounds just goes back to the offensive. The touchback in the end zone creates a big incentive for the defense to just let the ball go out of bounds, or encourage it to do so. Makes it way easier for the D to recover fumbles in the end zone, which is probably not intended by touchbacks rules.
They also tend to be really ugly or in styles that look weird on many doors.A friend of mine moved into one of these super modern industrial style urban apartment buildings, and they all have keyless locks. It totally works there, but if you have some conventional style wooden door, a lot of them look very out of place.