In the wild the shrimp strategy is survival over growth – to reproduce for continuation of the species.
On a farm domesticated shrimp are not healthy shrimp that would flourish normally in the wild.
Farmed shrimp are geared to fulfil a particular, limited purpose, not to live a full and rounded life.
Increases in growth rate, which would be irrational for a wild shrimp, make perfect sense in a crop, because crops live for people, not themselves.