It gets region locked for financial reasons. There are instances where the same game costs more in one region and less in another - shipping said games would be cheaper, especially in high quantities, and that increases the sales record of one Nintendo office while it lowers the sales for another - for example, a game available cheap in Europe and dearer in the U.S, imported from Europe makes a notch on NoE's post while it "nicks" some income from NoA which naturally expects gamers to buy American games.
The system is introduced to preserve the current infrastructure on the company - it's not validated by any technical reasons, it's all business.
To put it in perspective, you'd have to devise a way to bootload a game "through a game" and somehow map memory for the one you're trying to boot - in other words, create a ROM loader. Even if you managed to do so, it would be buggy as not all games require the same privileges and the one you're trying to boot would have to use the same functionality the game you're using for the exploit uses or less, thus crippling the whole system...
...unless you devise a way to remove the cart and re-load entirely, passing the result of the previously-performed region check... which is possible, but only with very in-depth system menu knowledge, and if you have that (meaning, practically kernel mode access), you might as well release a system menu patch.
That, and GeckoOS had the upper hand - Wii's functionality was strongly based on the Gamecube, which was thoroughly hacked. Here, the DS Mode is sandboxed, not to mention that it's nothing like the 3DS Mode, so it doesn't help much.
