I think the point is that a regular body weight routine is harder than using weights. If you're sedentary, doing a push-up is like starting out with bench presses that are more than half your bodyweight, finding an inclined surface to do push-ups against is not always possible, and using your knees can be painful, whereas if you're in a gym you can go bench press the 20kg bar or lighter dumbbells and know exactly how much weight you're using each session. Doing a chin-up on a tree in the park means you can't grab an assisted pull up band or use a machine to help you, so you're stuck trying to scramble up the tree with your feet + use bad sideways technique then lower yourself down slowly, which is risking injury.
These concerns are especially relevant for the elderly.
By the same token, a lot of sedentary people with no lifting experience might be intimidated by the idea of going to a gym, and the cost and even just the step of getting to a gym are additional barriers they have to overcome.
Getting started with a body weight routine or simple bands or kettle bell setup at home has huge advantages.
Just a note that swinging kettle bells, à la the simple and sinister book caused medial epicondylitis for me (buggered up the tendons in both my elbows). This is taking a long time to heal and limiting options on other exercises I can do that involve even a moderate grip.
My recommendation would be to rent a rowing machine and try that first.
To each their own, of course, but there are lots of ways to modify bodyweight exercises to accommodate even the most sedentary. I wouldn't exercise half as much if I had to go to the gym. It's less convenient for my WFH lifestyle and more expensive.
Edit: I should also say that I use weights like dumbbells and kettlebells at home. Not needed to start out, but very helpful.
Both options will require some research to tailor fit which progression level works best for an individual. Taking push-ups vs bench presses as an example, knowing that one can start with either wall push-ups or an empty barbell, I reckon the wall push-ups has much less friction than the other.
These concerns are especially relevant for the elderly.