Russia is impoverished. There's no way they could afford to sponsor a pavilion. I was there two years ago, and it was a very sad place. Other great candidate countries are facing similar economic crises, including Greece, Brazil and Egypt. Most of the Pavilions were sponsored and built when the Cold War was still going on, and economic barriers between countries were much higher. The end of the Cold War meant that having allies was no longer as imperative for countries, and the lowering of economic barriers meant that foreign countries no longer needed a big time Epcot foot in the door to help make connections in America. Put another way, the incentives for countries to plant themselves in Orlando is no longer as advantageous. Sadly, I do not think Disney will have an easy time adding pavilions for the foreseeable future.