Duckett gets away with more because his average is still over 40 and he also has a good first class record to back it up, Crawley has a fairly unflattering test average along with a terrible first class average.
Pretty sure I posted it during the first test where someone reported he had scored single figures in like 40% of his test innings, which regardless of the occasional very good innings he has makes him a massive luxury player.
Pope is a strange one, bit like Rory Burns where they do very well in County cricket but don't seem to able to really kick on at test level.