Why are so many healthcare workers morbidly obese when they were the knowledge and resources to correct this?

Many factors. I agree with dr. Michael jones. Behavorial change is possibly one of the hardest thing to train and maintain. It's much simpler to sit down and eat a tasty meal from a restaurant than to spend time cooking things from scratch that might not taste as good. People do things that make them feel good and often time, those are things that are not too good for you healthwise.
It's because this... ...Is not a knowledge issue. Almost everyone on the planet knows how not to be fat but we desire those things that tend us toward obesity more than not being obese. It's a choice issue to a very large extent (even in those with a genetic propensity). Here's another one: why does more than half of all respiratory therapists i've ever known smoke?