Why are gravity rigidbodies so performance costly?

I’ve read that rigidbodies are costly, but rigidbodies with use gravity checked are just a performance killer on their own, especially on mobile. I have tested it and can confirm that the gravity has a huge performance impact. So my question is, why is gravity so performance costly, and how can I simulate it without as much of a performance hit?

The same setup has a huge performance hit when all that changes is checking Use Gravity? That’s super weird. Good news is it’s not hard to do manually, just put the following in FixedUpdate:

rigidbody.velocity += new Vector3(0f, Physics.gravity*Time.fixedDeltaTime, 0f);

If that doesn’t solve the performance issue, then it’s not the gravity alone that’s the problem.