The biggest issue is that so few manufacturers now offer .20, Theoben were major supporters, AA have never made one, HW they're special order & take forever to be delivered,
so the majority of shooters will never be able to even try it, to understand how good it really is
For
Hunting at sub 12 it is the ultimate calibre, surface area & weight just happen to be spot on for the power level, so it's very efficient with air use,
it has a better BC than either .177/.22, retains a higher % of initial energy at range than either .177/.22, transfers a higher % of that energy to the target than .177/.22.
Lots of people make a big thing about pellet choice, but there are probably a dozen or so, it's just that every barrel seems to be single hole accurate with either FTT or JSB so why do you need anything else ?
Finally of course when you've got 'fingers like pigs tits' the pellets are that little bit easier to load