EDIT: Apologies for the rant, went a little overboard oh well.
For the overwhelming majority of heavy hitting chronic diseases (Diabetes T2, Obesity, Heart Attacks, even likely cancer). They are completely preventable though diet and other lifestyle changes.
Good food, grass fed meat, fish and fresh vegetables aren't that expensive people could afford it if they thought it was an actual priority. For those suffering from weight problems (In the UK the obesity rate is 27%! [1] Not even the overweight) I'd recommend for them to cut down on their frequency of meals and ensure that the one or two meals they have are healthy (Very low fructose, nutrient dense, keeps insulin low e.t.c.)
It's the same with exercising, a gym membership isn't that much money cheap gyms exist. But you don't even need any money to do some simple body weight exercises, depending on what you do and your fitness level it can literally take 10 minutes.
So it's not a lack of time or money for anyone but the absolute poorest, people just don't seem to care that much. I really don't know why ?
[1] https://files.digital.nhs.uk/publication/0/0/obes-phys-acti-...