Think in terms of a car: Growth metrics usually measure velocity, not speed. They don't measure the MPH that you're traveling, they measure how fast you accele

Think in terms of a car: Growth metrics usually measure velocity, not speed. They don't measure the MPH that you're traveling, they measure how fast you accelerate from one speed to another. So in your example, the speed you're traveling (75k sessions per month) is staying constant (you're not accelerating), so your velocity (growth rate), month over month, is zero.