It was useful to get the previous search term preselected when re-opening the search popup. I think it used to work like that, but not anymore.
This is also a default behavior for browser address bar, browser search etc.
Just to make it clear, here is what I see in the browser search bar when re-opening it:
My previous search term is highlighted by default, so I can start typing immediately and it will replace the old term.
Closing as duplicate of