So, Windows has gotten very good at memory management compared to past iterations of Windows. And, that's not to say that maybe there isn't something hogging some memory somewhere, but in that comparison at least you have to understand that at least to a point, the more memory that is available to Windows and applications/games, the more Windows (again, to a point) will allocate to it. So you could have a system where running a specific set of tasks, with an 8GB memory configuration, the system is using only 6GB of RAM, but, put 16GB of RAM in that same system running that same set of tasks and Windows might allocate 8 or 10GB for the same exact processes.
What's the difference? One of the system is going to complete it's tasks faster, smoother or simply more background tasks at one time, than the other system. Windows tends to not allocate more RAM than it reasonably can based on what's installed so that it has enough to leave a buffer when possible. If there is more available, it can allocate more without fear of running short on memory.