For dealers here the calculation of slabbing is profit-related: they send into slabs those they figure are the best looking coins and try to sell globally for people buying coins as investment. It is noticeable that few rare coins that do not look nice do get put into slabs.
What changed and is having an impact is more people buying coins believing they are an investment. But it is a cyclical change. I have seen it before twice.
Dealers know very well when they are selling fakes and avoid sending the fakes that are obvious by look to be put into slabs. Fakes that are hammered fantasy types they send, and they get slabbed. Those companies know only the mint histories of few countries.I think they can be good on moderns but never on medieval or ancients.
They way the world is going I am now convinced we will see many gold and silver coins melted. Common stuff but it is a loss to numismatics. And the price of difficult coins just keeps going up. I am finding more joy in copper now. They have the same history value.