The gains in size you make regardless of being on cycle or not are made and supported because of what you're doing to your body, which includes training, nutrition and supplementation. Gear is included in supplementation.

If you are at your natural max, meaning you can't really grow any more muscle tissue naturally, when you take gear, although you're still doing the work, the work is supported by the gear. Take away the gear and you take away the support system. No different than if you make great progress with great nutrition and then take it away.

Long and short, there are thresholds in everything in life.