Greek Restaurant?
OH!!!! The Odyssey??
That wasn't a Greek restaurant. It was a pretty standard Counter service with the usual burgers/fries/pizza etc. It also featured a stage which the Fab5 in their "Futuristic EPCOT Center" outfits would come out on and visit the tables.
Between the way Character interactions have evolved over the past 10-15yrs due to the crowds, and the simple fact that the Odyssey was pretty standard food available at any number of other locations and not really well placed for foot traffic, It ultimately became redundant and not really worth keeping open on a regular basis. (I recall back when it went Seasonal).
I will however say that the Odyssey isn't the best example of Disney's wasting something by letting it remain empty and not choosing to either demolish or repurpose the space. For starters, the Restaurant really wasn't anything really special. Between the Electric Umbrella and Fountain View you already had plenty of counter service options with similar food nearby, and much more conveniently located. The closure of the restaurant wasn't really a major loss. (The Character shows had already been mostly discontinued due to changes in the way the characters appeared, and the lack of guests eating at the restaurant).
Next, It's off to the side where most people didn't even notice it, and the building doesn't really stand out to constantly remind you of what used to be. (the had to let the trees around the Wonders Pavilion grow out to try and hide the building so people wouldn't notice it).
Then there is the fact that I personally think they've done a pretty decent job repurposing the space. True, It's often closed to the public, but it is used on a pretty regular basis for private functions. It could be receptions for a Disney Wedding, or corporate events/rentals. They've also used it during some of the festivals for events. The Restaurant's size is very well suited for these kind of events, so it's a very efficient use of the space. Compare this to WoL where you can't help but notice how empty and sad the place looks when decked out as the Festival Center.
And the Biggest factor? Pavilions like Wonders were just abandoned and left empty and unused for years. The Odyssey has never been truly abandoned. While they did close the public restaurant in the building, there has always been life within the building. Not only are the bathrooms located there still in use, but EPCOT's Baby Care center is located in that building. Backstage is also the employee Cafeteria which had always shared it's kitchen with the Odyssey.