Shorter trains means more trains, which means more train crews are needed to operate them. That's expensive, and they may just not be available. They have per-day and per-week hour limits like airline pilots or truck drivers, so they can't pick up extra trips even if they wanted to. And it's another one of those jobs where people are aging out and there aren't enough younger people coming in. There's an expectation that trains will be automated at some point, but we aren't there yet.