Well. this has been discussed fully before but:
A divot is not ground under repair.
Ground under repair is a hole made by a greenkeeper, or unusual damage to the course, or anything so declared by the committee.
Divots are not made by greenkeepers.
They are not unusual damage- they are a direct result of playing golf. Unusual dmamge would be, for example, a rut made in soft ground by a vehicle of some sort, something that is not, sahll I say, generic to the course.
Because they are a normal part of the game, they cannot be declare GUR by the committee.
I personally prefer that the divot be replaced in tis hole. However, some grass types and soil conditions heal better if the divot hole is filled with seed and soil mix. Thye holes must be repaired for the health of the course. When P. Stewart complained about the sand filled divlt on hole # 12 at Olympic, he was hitting a short iron, I think he would have reacted differently if he had to hit a long iron- in fact he would have praied god that the divot had been filled.
Of course the USGA and the Tours and etc. are always trying to find better ways to do things- in this example create a better way to fill divots that provides a better playing surface- but the point is we still must play the course as we find it- divots, divot haoles, sand filled divot holes, and all.
BTW, the green has always been treated differently in the rules. Shots "through the green" are played primarily through the air, whereas shots on the green are rolled along the ground. That's a pretty significant difference, and more than justifies what some might see as an "inconsistencey" in the rules.