If they have to explain what they are doing to novices, they may have to stop and artificially break it down into subtasks. Often they feel uncomfortable teaching the separate steps because they know they are teaching some bad habits. They are teaching the novices to do the task in a choppy way. In the short run, though, this task decomposition makes it easier for the novices since they do not have to worry about the big picture. They just have to remember the steps. As part of their mental model of the task, experts know various tricks of the trade, along with the conditions for using them.
Again re process being a crutch and why it's hard to describe process in a complet, conditional, nuanced manner. I know I've felt uncomfortable simplifying a process, having to leave out the many but rare edge cases and contingencies.
