For me I'm really not interested in "finding motivation" for what's only a fun pastime. I have time where I have to be somewhere, have to be doing something - like work, grocery shopping, laundry and everything else - and then I have free time. I savor my free time and I do what I feel like doing. The end.
I fell off RC a few months back. I realized I was earning too much money to keep living in a zoo, I immediately knew I was moving and where I was moving too (another specific Brooklyn neighborhood). Pretty much at the same time I knew I needed a new bike that would be just right for the riding I do and be long-term dependable, not a "curbside find" beater project. The move + the bike left no time for RC toys. No sweat. I didn't feel like RC planes, I had more important things at the time. A little while after the move it suddenly came back. I would have been just as happy if it was a different interest that found itself in my crosshairs.
If I had a buddy next to me asking these questions I would say: No need to force anything on your time. Go where your heart takes you. Or is the question really about lacking interest in anything, planes or anything else? That's a state of depression, most likely temporary. Or there are some pretty big issues inside your head right now, not letting you let loose and relax. Hey if you need time for yourself to try to find your way or settle your head somehow, then do that. Take a walk around the block or over the next hill. Find the right person to talk to. Don't do planes if you're not feeling it right now.
I had a period of many years where I was unsettled with my life and where I was headed. Subconsciously I refused to allow myself time for constructive projects like this. That's ok, that was then, but I'm glad I got over it or settled my head or whatever. RC planes are fun.