@Manoj_reddy When you sum up , you have the answer.
1. OS consuming more memory, as you are not often clearing your Recent Tasks, So the memory shall come down , when there is a crunch met.
2. You Pixel Launcher tasks around 300 MB.
3. I wish , you understand, Android apps are running in managed environment, we can't force the Memory cleaning, it is taken care by the Operating System.
4. Having said that, Android O has better memoyry management, it shall not allow these many apps to exist in parallel.
5. And what is the impact of this, do you see any sluggishness, still you have around 700 MB of RAM storage left.
6. If you are playing some games, then i would advice you to clear recent tasks, which would free some RAM.
7. So its a trade off between Smoother experience with few apps open (or) have too many apps open at the cost of more memory.
8. 3rd Party apps taking more memory is not in our control, as per android policy, an app can have 500 MB of max ram is what my understanding.
Hope you are answered.