Partly it's just a commitment you have to make with yourself to keep your legs moving. Also you might be pushing so very hard on climbs and cruising that you simply need to give your legs a rest.
I don't like coasting either. Unless I've gotten to a speed where I'm spinning a uncomfortable high cadence, I like to keep my legs moving. But when I am dead tired on a ride you will see me coasting more.
That said, I've found myself coasting more this year. So hopefully age isn't making me weaker.