I doubt the fumble is a major issue with Luepke. I think the issue is simply he’s a better blocker than ball carrier. His value is in his versatility to line up all over the field and be decent at everything.
The problem with feeding Luepke the ball even 5-10 times a game is you’re taking the ball out of the hands of better players. You have a better hard/physical runner in Williams and potentially Mafah. I think you’d also rather not waste those designed plays to get guys open in space on Luepke when you can use someone more explosive like Turpin.
Luepke played around 30% of snaps last year, I’d have to think that’s about the ceiling for Luepke unless we see a major injury situation pop up for this team.