Most of the time I just run my B Sport in Mod.. its an easy way to get two classes in. I suspect however that some don't like that or would rather have a mod boat incase one gets wacked. I get it.
Mod power is not cheap. The boats available (just call and buy one) to control that power are far and few between.
The last CMB 21 OB I raced was close to a 600 dollar bill fully setup (let me think.. that was 2004 as well). Sport motor.. 400.. a good sport tunnel.. 48mph.. a good mod tunnel.. 54 mph (lower for most).. 200 bucks for 6mph (proly not much more MPH).. tough one.
I do however like to tune a mod tunnel. Lots of challenges and all good. Im not sure in this day and age I am typical however. Most just want the darn thing fast and winning. Maybe its always been that way. Or when the going gets tough they get out.. I don't know.
I suspect however that the largest factor is products available. Limited choices.. never a good thing.
Grim