They can be maintained as long as you are willing to follow the science that it is to keep them. At some point people may get tired of it, get older, not care as much, so they relax on all the effort it takes. This is a look and lifestyle for those who are willing to put in the continued effort. Yes, once you stop trying, gains will be lost. To run a cycle (or 3) and expect that to be the end of the road like , "Hey I got all this muscle til I die", is crazy talk. It is a continued effort to maintain it. Period. When you don't want to anymore, it dwindles. And if you get so deflated mentally in pct it's no wonder there is no burning desire to hold on to it. I personally have never felt this way in pct where I was so depressed I let myself get fat within a couple months. Do I understand that one day, probably in my late 40's or so, will I be tired of the constant hustle to build and keep muscle? Yeah, I will get there. But until then I will follow the protocols required to build and maintain. And look friggin good through my middle age. If after that it's gone....see ya. It was fun.
And this is not limited to PH's. You can't logically be considerate of your health and do them for a decade. But for the time that I will do them I will assume the risk and protect myself to the best of my ability. After that there are a gazillion natural options to keep my fuel burning and body changing.