RJ,
Not answering for Mike - but in my opinion there are a few factors.
The main one for me is the use of Legend Couch grass on a few sandbelt courses. It's a very thick, broad strain of couch which the ball sticks in and provides no run. The disadvantage of this is that it takes many hazards out of play where the ball would normally run into them - this is especially the case on dogleg holes and holes with movement.
It is also an awful grass for green surrounds, and really takes the chip and run shot out (and putt) of the equation - as well as stopping you from bouncing approach shots in to greens. It also takes some skill out of quality ball striking in my opinion, as the firm tight lie is one that separates ball striking ability.
What legend couch does do is add effective length to a course, which can be a good thing. However the negatives far outweigh that positive.
Most obvious example is Commonwealth, which has thick legend couch now. It is not a sandbelt-conditioned course any more, it's definitely parkland conditions.
Another big difference in the last 10-15 years has been the use of machines to rake bunkers. Sandbelt bunkers all used to be firm and you didn't even need a rake 90% of the time - just a brush with your foot used to repair the bunker fine.
As far as greens go, most clubs that have adopted USGA spec green profiles over the last decade have been having trouble keeping firmness in the surfaces which does effect the 'sandbelt' conditioning model that most associate with. The increase in traffic also has an impact.
Competition for members in the sandbelt area also has seen clubs over staffed and overly concerned with green grass, as unfortunately that is still seen by most as the best test of conditioning.