Do you? Most of the time, when you open 5 or 10 apps, the one in the foreground is running, while the others are either sitting in RAM not running, or have been killed by Android. (Android apps have to always save any changes, so a killed app can be rerun with all its saved state when you bring it to the foreground, so it looks as if it was always in RAM.) Music apps are a special case - "close" one and the music keeps playing - because the app is actually running.
That's why RAM managers are bad for Android. Android does a much better job of managing its own RAM.