To address the OP's question, it all comes down to having a business case. The capital costs and operating costs must be justified by a plan that shows a healthy profit. Apparently, the financial planners at Disney were able put together a business case showing that MyMagic+ would be money well spent. Apparently, they haven't been able to come up with a compelling business case for a new World Showcase country. It's not that Disney can't come up with hundreds of millions or even billions of dollars. It a matter of where to invest. And profits earned at the theme parks do not have to be invested back into those parks. Not true. Back when Disney was planning and building EPCOT Center, the plan was the countries would sponsor pavilions, just like at world's fairs. However, that never happened. Not one of the original World Showcase countries was sponsored by a national government. That's true about Morocco being the only World Showcase country sponsored by a national government. Norway had some limited government involvement, but that ended long ago. Most of company "sponsorships" could hardly be considered true sponsorships. For example, there wasn't anything like "Germany Presented by Lufthansa." It was more like Germany, where the shops sold some branded products from Germany, such as cookies made by Bahlsen; or France, where an outside company operated the restaurants. Yesterland has an article about World Showcase that includes a list of the original participants:
http://www.yesterland.com/worldshowcase.html