I'm really curious about this. I've been on induction levels of carbs -for optimum health reasons not weight loss - for over two years. Every day I have more energy, better skin , fewer painful old sporting injuries. My Mum is really suspicious because she thinks low carbing is really dangerous, yet can't believe how well I look when I see her every month. Low carbing is a no brainer for me . It is obviously the way I was designed to eat. I was always really careful about what I ate before (the whole complex carb/low fat nightmare) but I was always hungry and got sick (flu, colds etc. just like everyone). I haven't been ill since I started ditched the carbs. Everytime I hear some talking head rabbiting on about how important a food group carbohydrate is I just chuckle.
Anyway I was a real gym junkie before low carb (usually twice a week -weights/cardio), because otherwise I very quickly lost all muscle tone and lost weight. I noticed within a couple of months of replacing almost all the complex carbs I used to eat with fat ( and most of that saturated) that I seemed to be putting on muscle really easily. I've never wanted to be musclebound , just fit and strong looking ,so I started to cut down on the intensity of the workouts. Now I never go to the gym. But I'm still very gradually putting on muscle. I still do 20 proper pushups a couple of times a week and I do plenty of yard work.
I'm sure cyclic ketogenic diets work and probably are the quickest way to pile on the muscle, particularly if you're not prepared to teach your body to be really happy with just fat (even for really high intensity exercise), because it admittedly takes a long time. Heck it's taken me two years and I don't think I've even come close to the true long term health and physique benefits. But I think carb 'refeeds' are stressful for your metabolism and completely unnecessary if you just want to be strong and fit. It's taken me the whole 2 years to feel as well as I do now and I wouldn't go back to carbohydrate metabolism if you paid me.
I have no idea why I build moderate muscle apparently without even trying. My own personal theory , for what it's worth, is that prolonged severe carbohydrate restriction has made my endocrine system so healthy that I've restored normal production of human growth hormone.

So I'm not saying that C.K.D diets don't work, but in my experience anyway, the theory that ditching the carbs long term necessarily causes muscle loss
is hogwash. Or maybe just a plot to keep up gym memberships
cheers