There's a difference between being able to operate a new system day-to-day, which you may have been trained for, and being able to work around a system you've been using for years and know all the back routes in.
We have a mission critical but old, command line system at work. It's massively reliable (a few minutes downtime in three decades), fast and really efficient for those trained in it but management can't cope without drop-down menus so is being replaced with a much less reliable, much less capable Windows app. Thank's for nothing Steria.