And time and energy are infinite, right.

It doesn't take more time to eat less, but for exercise it is simply a question of priority. Yes you will have to find some part of your day where you do something you value less, then take the time to exercise instead of doing that.

It's great that you have the privilege of sufficient spare time to allocate towards exercise and the luck to avoid any conflicting medical problems. Investing in your own health with regular exercise and an improved diet will hopefully lead to fewer problems later in life.

However, please remember that some people are not as privileged. Free time is not always available. Good food - and sufficient time to prepare it - isn't always available either. Life is complicated and work, kids, and other important obligations take priority for many people.

> Eating less costs less.

Eating less doesn't always lead to better health. Nutrition is complicated.

> there only question is if you want it or not.

Do you also tell people with a broken leg that they could walk if the wanted to? Staying healthy is not a matter of willpower and/or education. Staying healthy isn't even deterministic, because our knowledge of medicine, nutrition, etc is still imperfect.

> You don't need a gym, even to get into seriously good shape https://www.reddit.com/r/bodyweightfitness/

/r/bodyweightfitness is actually pretty hostile to low/no-equipment approaches. It should tell you something that the top comment on a "Jail for 3 years - training with no equipment" post leads with "you might have access to a gym".