Prison RP on LS-RP wasn't non-existent. It went through periods of inactivity because it's a niche within a niche. Not everyone finds prison RP enjoyable which is completely understandable.
Jail RP here is the same really. There's always people there but the lifers go through spells where they don't log in so it's mostly tourists. There's politics, there's fights and there's plenty of passive roleplay. A lot of times there is a deputy in-game as well.
It's active but the roleplay can be a little lacklustre at times.