Is it discouraged or is it simply an option that nobody takes?
Just curious.

Largely a personal decision, but also depends on what cabals you're interested in helping.

I've done it both ways and I personally preferred sticking with a persona that had a lot of history/backstory because a) it takes me a long time to wrap my head around the character, and b) I don't think you get the same kind of character development or evolution from a random pop-up IMM persona (again, just my opinion/experience). Obviously a lot of people are fine with a new persona, and that's what most IMMs end up doing.

Gr

Most people have a plan in mind for a religion and/or cabal they want to oversee that is different than the cabal/align/religion that they had when they heroimmed. It also helps to get a better clean slate so to speak in the way that the persona interacts with the mud since they have no history to speak of with current characters that they leveled with or inducted into a cabal or whatever.