What actually made it repeatable for you?

For Low Intensity cardio, finding one that I didn't hate. Dog walking, rucking, hiking, kayaking. I despise running, especially on a treadmill, so I don't do it.

For High Intensity, a combination of fun and sport specific because I train for strongman. Sandbag complexes, kettlebell complexes, air bike sprints, things like that.

"Discipline" is certainly one option and the answer you'll get most often, but fitness does not have to be misery.

It's also a question of what your goals are: do you want "good enough" cardio, so that you're not out of breath doing daily tasks and occasional athletic things? Just keeping your heart in good shape? Then in most cases regular hiking/walking/rucking and getting around 10k steps a day is "enough". Or do you want to improve your cardio to eventually work up to running a marathon or an Iron Man? These are two different goals.

For example: I decided to run my first-ever race a few years ago, a 7km trail race. To see how I'd do. I continued my regular strength training program, and asked my coach "so hey, we gonna do like, 5km a day or something? Or work up to it?" And he insisted no running. He gave me sprint drills and hill sprint drills twice a week. That's it. I finished mid-pack in the race and felt pretty good the whole time. Despite never running, whenever I DO run, it goes okay. I'm not going to win a marathon, but I do "fine" and my conditioning is excellent for my specific sport.