It's impossible to keep everyone at a 80-90% busy rate at any large company just due to the inefficiencies a large system accrues, idling is embedded due to the many layers of communication, coordination requirements, etc.

Also, let's add another charitable explanation to this:

As people acquire more experience in the org, they become more efficient. That means someone who was maybe idling 20% of the time is now idling 50% of the time - they are simply faster and better at doing their job, but for whatever reason they haven't been promoted yet or assigned new responsibilities.

I don't know whether this is "good" or "bad".