The phrase likely arose from the fact that gravy is a tasty and flavorful addition to a meal, making it even more enjoyable. It's something extra that enhances the experience, just like something unexpected and positive does.
Therefore, saying something is "gravy" implies that it's a pleasant bonus or something that makes a situation even better, even if it wasn't originally part of the plan.
Here are some examples:
* "I got a raise, and then I won the lottery! Talk about gravy!"
* "The project was already going well, but then we got extra funding. Now it's all gravy."
So, while "gravy" may not directly mean "easy," it implies that something is good, fortunate, and makes a situation even better.