There are 2 reasons for this,
The first is machismo, people buying
clubs with the stiff shaft cos they think they are strong enough for them, find out they arent then try to sell the club on cos they cant use them.
The second is that most manufacturers sell their premium product with a stiff OEM shaft because their regular shafts are like putty and no decent player who uses a manufacturers top product would use the regular spec.
Standard fit shafts on most
clubs are pretty soft, if you are using an OEM regular shaft then you probably would go to a regular in an aftermarket shaft (Graf Blue, Aldila Green etc). Stiff OEM shafts are closer to firm and would probably suit the vast majority of players.
The Fujikura REAX shafts on the new
R7 are pretty good, more like stiff than firm. I dont know the Adams Redline range at all but I do know the shafts they were using on the tight lies range were pretty average.
D.