It's easy to say, "Oh, I work 10 hours a day then I have to go home to my family", yet I still find time to play stupid phone games, browse HN, and watch the Olympics.
Sometimes I get on a kick: I biked to work (~8 mi.) a couple days a week in the spring. I've started Couch-to-5k a couple times. I did muai thai for about 6 months. But it peters out. Apparently the gym downstairs at work has a personal trainer, and I've been talking about setting that up for months. I feel anger (and let's be honest: guilt) any time anyone tries to "motivate" me by encouraging me to go to the gym or exercise.
Recently, I've had luck with biking on local errands. It's easy enough to throw on a backpack and pick up groceries 0.5 mi away rather than drive. And walking the dog forces me to at least go outside.
So clearly I haven't cracked the problem. But know you're not alone. And the best suggestion I have is to do something, anything... then try to do it again the next day.