Welcome to Android Central! Keep in mind that this is how Android works. Android isn't like Windows, where it's beneficial to close every app you're not using. In Android, empty RAM is wasted RAM. It's more efficient for the system to keep certain apps or services open in RAM, many of them cached in the background (and therefore hardly using any CPU or battery).
Also keep in mind that there are a lot of system processes that have to run in order for the phone to work correctly. If you feel that's not how Android should work, then perhaps you should study to be an Android engineer and apply to Google so you can change it to how you think it should work? Or perhaps you would better understand why it works the way it does.