Ime is a rookie coach whose team struggled a great deal in the first half of his first season. Things started to tighten up as soon as he knuckled down and implemented basically a 7-8 man rotation while giving virtually zero minutes to any of the younger, less proven players on the roster.
I would not expect Ime to loosen up the rotation anytime soon. Basically as long as he's still figuring things out as a coach he's going to lean heavily on veterans, even if that doesn't really make sense for the big picture / long term outlook. You absolutely need to have more than 7-8 guys who know the role they are expected to play and have gotten enough reps to be relied on as necessary. Even in the playoffs, you might not actually play more than 7-8 guys in a game, but you shouldn't expect to be able to lean on the same 7-8 guys for an entire playoff run.
It's a pretty normal thing for rookie coaches to rely heavily on vets, I think. Brad did it too a lot of the time. Ime is in a tougher spot than Brad was because he (1) had no experience as a head coach prior to starting and (2) he took over a team that is actually expected to win.