[Retric]

In an ideal world you might have a point.

However, PHD students on average are very far from world class. And in just about every case they are simply looking at a problem so unimportant that nobody considered it before, and most likely nobody will ever look at again.

It's almost always a waste of time for both the student and everyone else involved.

PS: There are plenty of counter examples where PHD research happened to be valuable, but that's a tiny minority of cases.