There are plenty of people who are naturally thin, but not healthy.
I'll be honest, my main motivation is to look better. I want to fit into my clothes and I want a little less jiggle.
BUT- I also miss feeling strong. Three pregnancies and three c-sections in 4 years has absolutely wrecked my body, and I started feeling old and out of shape for the first time in my life.
My husband and I are back on track though, and hitting the gym again.
So, to answer the question, I want both. Ask me on different days, and I will probably give you different answers.