I think the answer is Duration. A lot of us stay on at least HRT doses. After gaining on cycles, PCT, inevitable moderate crash and recovery, it's too up and down. Moderate doses (or in my case actual HRT all the time keep ya growing with no crash and lower risk).
So, rather than do this bouncing up and down, I've run an HRT dose for many months now, about a year, and no higher. And I mean a real HRT dose like 150-175mg a week. My T levels hover around 1000. This has been the best year of training out of the last several and at the same time one of the hardest years of my life. These gains while "cycling" + this year's trouble would have = no gains if I had been cycling.
Low dosing also allows you to adjust to life's problems, diet mistakes, periods of high stress and lack of sleep that would ruin an 8 week cycle.
In my case I was running 8 or 10 week cycles of 5-600 Test with an oral on the first four weeks. Basic old school (I'm 37, been training for 20 years.) Then come off, do PCT, crash to some degree, stay off a while and do it again. (no matter what anyone says, no more high levels of test, you retain a few lbs but lose the rest if you're off long enough. Shit comes up in life...one or two weeks of bad dieting after a cycle and there go your gains. Genetic freaks aside.
JMO.