I was under the impression that this is an (undesired) side effect of how it works under the hood.
As in, the bounty system has a difficulty level ranging from 1 to 10, that determines what bounty types are available, and how big they are within those types.
So, "give easier bounty" sets the difficulty level lower, "give harder bounty" sets it higher.
But within the same difficulty level, you can have an easy bounty type (e.g. pirates) and a hard one (e.g. Remnants) which aren't controlled by the dialog options. So if the normal bounty targets Remnants and the hard bounty targets pirates...