That's a bit shit if true, hope it isn't.
They really could have stepped up with new technology, not like they haven't had time or money or need to do so.
You can continuously improve an existing engine though, you don't have to build a whole new one from scratch. In fact if an engine is well made you can completely replace parts of it like the renderer, editor, audio middleware, etc, without having to change too much elsewhere.
There's also the question of how much time do you want to invest in graphics, given that most increases in graphical quality result in more work for the content creators, who could instead be spending their time building a vast, open world.
