There's too many reasons to buy games now-a-day, but mostly I buy the ones that provide Co-op experience, so I can play with friends.
If the game is Single Player only, then I'll buy it for the story and gameplay.

most obvious pay-off of playing games. Beating a boss, leveling up, or creating a new weapon are all obviously “fun” for the sense of achievement they offer

If a game is good I'm more than happy to support developers and third party sellers with my money. Depending on if I actually have money aswell haha

Nothing motivate me because The Game is in my blood..  

The need to find a new virtual world that i will thrive in there, explore it and learn from it. I research a game and when I read reviews and see videos, if I feel that "thing" in me saying this will be fun then I know this is a game I will buy. from technical specs I admit that a nice presentation, good story telling and the existance of demo or beta are more important to me than ground-breaking graphics.

I dont think i need motive to buy a game u like   i buy games that i enjoy playing first i try it check game lore then if i like it i buy it  

First An awesome Unique Gameplay, Major Improvement in Sequels and out of the world Multiplayer experience just like Mortal Kombat X, Epic Story line and Graphics like Witcher 3
and Graphics!, Iceing on the cake    

I always think abaout the work involved in producing a game!

I whould purchase a game to try new stuff , i really like beautifull looking games that i could max out and look insanelly good , but I also appreciate games that doesn't involve too much FX but have a great story , mechanics , gameplay. I really like to try new stuff. Thanks Kinguin !