Why I cannot fully commit to gain weight?

As the tittle suggest I don't know what I cannot gain weight actively, I've put on the pounds? Yes , but I lose them after a short time because I go back to my old habits. Also I've made various weight gain challenges that I end up quitting after a week or less . I don't know why I do that, I enjoy all the aspects of the gainer life , the hedonism, gluttony, laid-back living and of course the softness in my body . Has anyone experience something similar?