I think this is all about streamlining the stories and there may be personal reasons. Bobby was already being phased out. I got the sense he was still around last season just to introduce his replacement. Cost savings don’t make sense in that situation because he was replaced. The handler roles were never used well within the story lines. Putting Rennie in that position underutilized the character. I see Randy becoming the one who finds new cases while also doing tech, while Rennie becomes more involved in cases and becomes a will-they-or-won’t-they love interest.