That is a good thing though, it means you PC doesn't need to use that much ram to run the games.
The differences could be in settings of the games themselves, the others might be running lower settings or different effects than you are. The true usage of the programs could be hidden in commits instead of ram, open up task manager and then the performance tab. Choose Open resource monitor from bottom and then in next window, choose memory tab and look at the commits as that shows how much of page file + ram is being used by each process
I normally use 4gb just sitting on desktop (that is with chrome open anyway) so your ram usage while playing a game is a bit low.
NBA 2k17 doesn't require much:
Recommended System Requirements below:
OS: Windows 10 64-bit
CPU: Intel Core i5-670 3.46 GHz or AMD FX-4100 3.6 GHz
RAM: 4 GB System Memory
GPU RAM: 2048 MB Graphics Memory
GPU: Nvidia GeForce GTX 750 Ti or AMD Radeon R7 260X
DX: DirectX 11
Additional: Dual-analog gamepad
http://www.nba2k17world.com/nba-2k17-system-requirement/
tomb raider
Using High quality textures uses a lot less RAM. Please note that the Recommended Spec for the game is 8GB of system memory, and recommended is aimed at running at High settings, not Very High.
witcher 3
Recommended requirements:
OS: 64-bit Windows 7 or 64-bit Windows 8 (8.1). DirectX 11 is necessary to run the game.
Processor: Intel CPU Core i7 3770 3,4 GHz, AMD CPU AMD FX-8350 4 GHz
Graphics: Nvidia GPU GeForce GTX 770 or AMD GPU Radeon R9 290
RAM: 6GB
Disk space: 40 GB
Witcher 3 should be using the most on your system