The player controller in that Contra game is extremely simple. Movement snaps and stops instantly, and the animation are simple. You stand, run left or right at a constant velocity, jump, and shoot in one of 5 directions.

Giving your character more movement possibilities tickles the brain with the complexity, enables more fluid and aesthetic movements on the screen, and increases the possible difficulty of platforming sections and boss fights.

Silksong has a very complex movement controller. The player has mass, can grab edges and climb up, and unlocks additional abilities as they play. Now they can dash, run, doing a running jump, wall jump, stall a fall with a float, and more. Attacks come in many flavors, with different styles enabling attacks of different speeds and distances and strengths, with different considerations to manage.

More complex controls take more investment for players to learn and are more rewarding. An extreme example of this is found in games like Monster Hunter, where each of a dozen different weapons controls very differently and takes many hours to become proficient in.

Elden Ring does not have an excessively complex movement system. You walk, run, jump, dodge, and have a handful of fast and slow attacks for a given weapon. It finds success through incredible world and level design and its difficult and rewarding bosses. The game loop is exploration, fighting difficult foes, and slowly growing stronger-- both through game mechanics of gear and stats, and through personal mastery of combat.

Soulslike games revolve around players gambling directly with arbitrary amounts of time-- when you die you drop your money, and if you die again before reaching that grave it's gone permanently. They make you bid the only resource that you care about: your hard-won progress over time.

Complexity and stakes deepen the intellectual and emotional enjoyment of a game.