Yes
It is easy to get wrapped around the axle on the slabbing issue and think that other collectors would certainly want copies of whatever issue slabbed. Simply because "we", or "most", "many", "some" of us would.
The truth is that their are collectors out there, who have zero desire to let anyone handle their books. And the thought of wrapping, shipping and letting strangers handle and critique their books is not on their radar screen.
Some of these folks are known, others may have finished their buying in the 70's, 80's, etc.. and moved on to other collectibles. But those books are there. Stored safely away.
Is their a glut of 27's hidden away. I doubt it, but 38's, in my opinion, were not considered that scarce 30 years ago.
I would say that only a small percentage of comics, and Golden Age comics, are slabbed. Most dealers and collectors are not interested in slabbing- you don't need to be 70 years old! I personally crack almost all slabbed book I buy, with some rare exceptions.