Not sure it's losing motivation rather than being confronted to one's wishful thinking.

If I have so many plans for when I retire early, how come I do none of it now? If that's really what I want, how come I don't spend at least a few minutes on it every week?

I don't have to find a 50h/week activity to replace my work. I don't need any activity that replace my work routine. I can simply take whatever hobby I had while working, and spend at least as much time as when I was working full-time.