Why isn't 100% contract volume equal to 100% utilized pipeline capacity?

We have all heard it before - "we meet 100% of our contracted capacity". Cool, sounds great, but what does that actually mean?
Does that mean its impossible for a pipeline to move any more volume?
What about maintenance? What about unplanned shutdowns?
How about difference in control room operators experience or comfort level "pinning" the system?
In short, meeting 100% of contracted volume does not mean an asset is 100% utilized. Some reduction from 100% utilization are necessary for maintenance - but what about the rest of the available capacity? I think pipeline companies can be more more ambitious within the bounds of safe and reliable operations to both serve their customers and meaningfully contribute to the energy transition today with increased efficiency.