-Like PMPM said, if you just do cardio you will look smaller but with your clothes off, it won't be a pretty sight. I had a big ass, hips and legs and when I lost all that fat if I just did cardio I would have a bunch of extra flesh. I'm pretty certain building muscle on my legs and ass has allowed things to get tight again, even if by just being bigger under my skin and replacing much of my fat with muscle.
-but the bggest reason IMO is progression. I have no idea how anyone in their right mind could tolerate a lifetime of doing cardio on machines. To me that is hell! But if you lift, you get stronger. You set goals and you meet them. You see muscles form and you feel them where you didn't before. Not massive ones mind you, but you start to get a firmness in the hips that you didn't have before, your forearms are harder etc. And then you see your strength go up and your lifts get better and better and before you know it, you are lifting weights that you didn't think you could ever! And it's you!
But on a machine, it's just putting in time. You just want to get it over with. In the long run, I don't think that is a maintainable way to stay fit because it is so much of a chore people wind up just using it to get 'caught up' when what is th eonly thing that works is a life long lifestyle change. This is what you do now.
If you cycle, swim, run or hike for cardio that's a bit different IMO. Those are activities that also work well with goals, progression and enjoying and being driven by visible improvement in performance.
So with that said, finding a cardio activity that isn't so tedious and allows for better progress definately helps. But if you are able to put on some music and zone out while jumping rope or using machine for ten minutes after weights that's good too.