The user needs to see the end message to tell if it succeeded (eg all warnings, no errors), that would not be visible if the compile output window scrolled to the top when complete.
But `next error` after the build is finished goes to the first error/warning so the user is able to read the build result and then look at the messages, so current behaviour meets the use-case at the cost of one click/keybinding.
As @dolik-rce points out the UI is not locked during builds and automatically going to the first message when the build is finished steals the user focus, which is generally considered bad karma. So at best it should scroll just the message window, but as I noted that hides the end status message.
This is the same with at least some other IDEs I use, probably for the same reasons.