Why do you kill in the games?

Disclamer- I have never played an ac game! Im simply curious as from what ive seen online the game has you going into simulations of past peoples lives to find where artifacts are hidden to get to them in the real world. If this is true then whats the point of playing out these assassinations on people if its just a simulation. I know this may be a stupid question but I cant seem to find an answer on google.