Why Aren't There More Nice 1975 Kellogg's Cards?

Other recent purchases included some 1975 Kellogg's baseball cards.  I knew from the listing that they weren't in great condition.  That seems to be the norm for 1975 cards.  Finding nice 1971s being difficult makes sense since there were no factor sets, but what about the 1975 factory sets?

Were there lots of 1975 factory sets?  If so, where did they go?

More about Tiant some other time.  I'm hoping someone can shed more light on the problem with 1975s.