The problem with this, for too many people, is that they've never felt "good". They don't have a point of reference they could use to guide them to a better lifestyle

They only know the right-now and that's good enough for them.

This is something I've seen with my friends and family who have never been in good shape. They don't know that it's possible to go up 3 flights of stairs 2-3 steps at a time at a brisk pace and NOT be panting with exhaustion afterwards. They don't know that it's not normal to fart 24/7 and have constant heartburn, because that's all they've ever known.