My personal experience as a man that once weighted at around 120kg, and now just sat down after a 30 minute jog and weighting at around 85kg, my perspective is that it is all about habits. Habits are easy to maintain and hard to break. For me thinking about it as a lack of motivation was actually counterproductive. I would try to "force" myself to start exercising, telling myself how much I sucked for not doing it, and it took me years to fully realize that doing that to myself inside my own head was actually part of the problem.

What I recommend people is that they start small. Do something small enough that you can actually be bothered. And preferably something were the distance from your couch is short. Which is why I started doing some exercise inside in my own apartment, and combined that with just going for a walk. At first I walked around the neighbourhood, maybe 10-15-20 minutes. A few years later I walked for two-three hours if the weather is nice. It's all about setting the ball rolling in the right direction. When I told myself I "had to" start working out I gave myself a bad conscience if I didn't work out "enough". What I didn't realize that is that every time I went for a walk, even a short one, going for another walk later became a little easier. Don't get me wrong I had many dead periods where I stopped exercising completely and fell back into my old habits. But after a while I would get back to it and for each time I began anew it became a little easier. Gradually year by year I shifted my habits from being very self-destructive to my new normal (which isn't perfect and I still work towards greater balance). The upside here is that for every kilo I lost, and for every walk I did, my health improved, my energy level improved, and finding motivation became easier and easier. Because now working out has become a habit, and so keeping it going require less and less effort.