So it isn't about discipline either, it's about habits?
I'm like you. Routine exercise for the last 25 years or so. I feel neither particularly disciplined nor particularly motivated. It is either just a habit I've formed or I happen to have the correct physiological temperament for exercise to be easy.
EDIT
I'll also add that most people who are disciplined don't really think about it that way. They just do what they need to do.
I claim the same about hunger (within bounds of moderation etc etc). It's simply uncomfortable, but it's a discomfort that you can adapt to and live with. My general view is that both hunger and exercise work as ways to moderate weight but they rely on the exact same capacity for discomfort (and enduring that requires either necessity or motivation/discipline etc)
I took a solid 6 months of forcing myself to ignore my mind's constant excuses to not work out, to the point of my mind realizing that the excuses just weren't going to work and stop.
Exercise feels good to me. I think it felt good immediately when I started? I like the feeling of pushing myself and I kind of like discomfort/pain I can control.