It's all about motivation. We all know we should work out more, but we don't want to. Oh sure, you can say "oh, I want to, but I don't have the time." Sorry, doesn't fly. Occasionally we really are too busy to squeeze a workout in, but in reality it's just that you aren't prioritizing it highly enough. To me that's really "don't want to" enough to find a way.
Why don't we want to? Lots of reasons, but I think a lot of it boils down to making ourselves think we have to. Get out of that mentality, and get out now. That doesn't help with motivation, it only makes it worse. You don't have to. Nobody is holding a gun to your head. But you probably do want to, or you wouldn't still be reading this. You just may be finding you don't want to enough to prioritize it high enough on the list.
One thing works great for me, and that is scheduled workouts with someone else. In an ideal world it's with a trainer who you're paying to kick your butt. Those are best. But failing that (because we can't all afford that), another great alternative is regularly scheduled workouts with anyone else. Why? Because canceling is a pain. You're worried you're letting your partner(s) down or that they'll think you're a wuss or whatever. It's peer pressure that works. Plus the time seems to go faster when you have someone to talk to. The drawback to the friend versus the trainer is that it's easy to not work as hard with the friends. SO WHAT. Something is better than nothing, and by a LONG shot. And having it regularly scheduled is really key, since it's much harder to drop the ball on scheduling the next one.
But what about motivating yourself for lone workouts? Step one is don't tell yourself you have to do it, because down deep you know you don't have to. Focus on the reasons why you want to, and do everything you can to find more reasons why you want to. The single best motivator is finding exercises that you really enjoy doing, obviously. That can take some effort, sure, but it's out there. No, not everyone enjoys running or bicycling or even tennis. But there are so many good sports that provide great exercise that you can likely find something you enjoy. Heck, I find spinning on a bicycle trainer works great as long as I have The Big Bang Theory episodes to watch while I do it. You might find a treadmill or indoor bike much more tolerable and quite possibly even enjoyable if you find something else you enjoy doing while on it. Podcasts, TV shows, etc. Or they might at least be tolerable enough that you don't mind doing an hour on the treadmill on a day when you just can't do a meet-up with someone somewhere else thanks to other commitments, weather, etc.
Oh, and if you're thinking "I can't keep up with my friends at what they do", stop that thinking NOW. If your friend invites you to run with them and the only thing stopping you is "I can't keep up", get over it! They know you won't be at their level. They'll adjust. They really don't mind, or they wouldn't have asked. Again, friends like to help friends, especially with this. Stop worrying about "bothering" them or "holding them back" or whatever. It isn't a big deal. If/when they need to train harder than you'd allow as a partner (say they're training for a race and want to compete), they'll let you know. But otherwise? Don't fall into the "I can't keep up" trap. It isn't real.
To reiterate, find ways to make it fun. Lean on friends to help you with that. Generally, you have similar interests to your friends, or they wouldn't be your friends. And if you have friends who do exercise, find out what works for them. People who exercise a lot do enjoy spreading the joy they've found in what they do.
Seek it out. All things worth having are worth working for. Get started.