[ncallaway]

It seems it wouldn’t need to be an intentional strategy, but could be selection pressure.

If it is an effective strategy, then scammers who have better grammar may find their scams less profitable, and move on to other jobs. While scammers that have worse grammar end up being more successful, so decide to continue.

(I’m not saying this strategy is effective, or that this is the mechanism that explains the relationship, just offering one possible explanation)