"Maintenance" workouts to not meet the requirements of overload.

"Overload" is working the muscle beyond the fatigue it is used to, if you continue to workout with the same volume and intensity, you fail to overload the muscle - many people say it "adapts" which is why "change things up" is often a popular response.

That's where progressive overload comes in, if you fail to increase the tension / stress placed upon muscle fibers, then you will not have anything new to grow from.

If you perform "maintenance" workouts, meaning do the same thing each week, you won't meet the requirements of progressive overload and you won't overload the muscle, eventually the workout will become less hard on your body.