Because it's more immersive.
> Having it be "realistic" doesn't actually make it easy or discoverable.
Isn't it the games job to teach you this? Like it's teaching you which button to use?
Realistic skydiving game: Start! Drive your civic to the DZ. Oh no there’s traffic! Wait for plane. Get in plane. Take 20 minutes to fly to altitude. Fall for 1 minute. There are no obstacles, nothing around you so you don’t die. Land. Wait to get picked up, take 1 hr to repack your parachute. Talk to your friends about how cool it was.
Fun skydiving game: Start! Jump out of airplane immediately. Skydive for 15 minutes. Surf on the wing of a plane. Avoid obstacles. Fly around buildings. Try to land in a swimming pool on the side of a mountain. Land. Parachute repacks automatically. You’re back in the air automatically.
As another case in point: movement speeds in most first-person 3D games are unrealistically fast (like, walking at 10 mph, running at 20+ mph), because realistic movement speeds would make navigating around the game world painfully slow.