When you pin items to the Jump List, they go to the top of the menu that appears when you right-click the Taskbar item. Why not put the pinned items at the bottom? After all, over 98% of users leave the taskbar at the bottom of the screen, so putting the pinned items at the bottom of the list maintains a consistent position relative to the Taskbar icon, permitting the development of muscle memory.
The Taskbar folks tried out all sorts of ideas for ordering the Pinned items, the Frequent/Recent items, the Tasks, and the system commands on that one pop-up menu. And these ideas were put to the test: With real users.
Usability tests are one of those things that every developer should go through. You think you've designed a system that is intuitive and easy to use, and then you are shocked back into reality as you watch user after user struggle with your masterpiece.
In this case, the usability tests revealed that most people look for the important items at the top of the list. When they went looking for their pinned items, they started at the top. And often, if it wasn't there, they simply gave up.
The resulting order of items (Pinned, Frequent/Recent, Tasks, system) reflects the results of these studies. Since Pinned items go at the top, that leaves the opportunity to put the system commands at the bottom so that they have a consistent location. For example, Close is always the last item. That's where your muscle memory can develop. The Tasks go next to the system commands since they act like application-specific extensions of the system commands. Tasks also do not change, so that permits muscle memory to extend further into the menu.
Once the other three items are placed, the decision of where to put the Frequent or Recent items is forced: It goes beneath the Pinned items and above the Tasks.
There you have it: The order of the items in the right-click pop-up menu for Taskbar icons. There's a method to its madness. And it was decided by you, the users.
Pre-emptive hate: Yes we know that you think messing with the taskbar button right-click menu was the stupidest idea on the planet.