Why do so many frum people take their health for granted and do little to make sure they stay healthy?
That assumption is grossly inaccurate. Frum people, more than anyone else in the world, do not take their health for granted.
How many others do you know that pray for their health at least three times a day? And there is no greater way to not be taking your health for granted than by asking He who grants good health to bestow good health upon you and your family.