I suspect the “all that much” is doing a lot of work here. I think I get it. Like, as long as my body is not malfunctioning or heading for a long-term catastrophe, I’m not motivated to improve it.

Malfunctions can be difficult to detect, if you're not paying close attention to your body. Our bodies have evolved to maintain homeostasis within a tight range, and can compensate for quite a lot of hidden pathology. Until you reach a threshold and decompensate, at which everything goes to hell and at that point it's too late to really fix.

They might mean it’s not a primary motivator.

That’s how I felt when I was younger and had a seemingly perfect bill of health regardless of exercise.

High blood pressure in my 30s changed some priorities.