Don't automatically activate the only opened song.. read why:

It is a pain in the neck!

You are working on your big project with trillions of tracks etc. and you are searching in older projects for “that special thing” - you have to acticate it - listen and when it’s not there, close the project. In that very moment Cubase automatically activates your big project again and you have to wait and wait and wait until you can proceed to the project you want to peek into (and listen).
If there would be switch in the preferences like “automatically activate only opened project” then I could decide whether to switch that functionality on or off. Usually I want it on - and that’s what people want. But in the above stated case - it is not helpful

Carry on guys! You rock!