I for one am not losing size training at home using mostly bands. I have trained for 35 years, the only time I lost muscle was during basic training in the Army, high activity, running, and 3 meals a day contributed mostly to that.
Training at home as long as I keep my intensity high I can do just about any kind of workout and maintain and even put on a little muscle size. Food and hormone levels also contribute to maintaining my muscle, I don't let my hormones tank and I keep my food on the high side (I don't diet).
How are you working legs just using bands?