Motivation only helps you get started. It wears off after the initial excitement has died down. You can not rely on motivation alone. After that, habits are the only thing that remains.
Do you need motivation to brush your teeth in the morning? To shower? To go to work? To sleep at night time? To eat three times a day? The answer is no - these things are just what you do to take care of yourself. Exercise has to be the same or you'll drop it the second bad weather, a late night, an early morning meeting, an injury or a mild cold interrupts your flow.
I can't tell you how many times I've started and stopped a regular exercise regime over the years because I relied on motivation alone. I kept getting to a certain point and losing all the progress I made when things got hard. It wasn't until I made a plan, set aside the time, changed my alarms and made the determination to show up every weekday dressed in my exercise gear and ready to go that I was able to make it a habit. After the first month, it got easier. By the end of the third, it didn't feel like I was making a special effort at all. By the sixth, it was like I'd been getting up early and exercising all my life.
It was consistent habits that made me put on the weight in the first place. I had to apply the same kind of unrelenting pressure in the other direction to take it off again.