Well it's challenging, risky, and there are always learning curves. Many think why put myself thru that adjustment period, it's already hard enough.
Most big keepers are from pre-varroa or near that time period. I can't say that I blame the commercial beekeepers on just wanting to make a livelihood but why not keep the majority with treatment and have 10% or so pushing towards a chemical free operation.
Big beekeepers are the best suited towards truly finding a fix on a large scale. Experience, quantity of bees, equipment, varied environments. These are the breaking grounds that are needed to test stocks and truly see what works and what needs done.
Mark how many big guys have truly tried?