According to Miyamoto, this is because the Nintendo NX features a rather important idea that if revealed, could lead to the competition stealing it. “In terms of NX, there’s an idea that we’re working on. That’s why we can’t share anything at this point, and I don’t want to comment on the other companies. If it was just a matter of following advancements in technology, things would be coming out a lot quicker.”
Miyamoto’s latter comments also seem to echo what was said earlier about how the Nintendo NX will focus more on the games and less on hardware specs. It is also in line with what Nintendo’s late President Satoru Iwata said back in 2015 in which he stated that by revealing the console too early, it could cause the competition to steal from them.
In any case details on the console are expected to be revealed this fall, but so far Nintendo’s decision to keep their lips sealed has led to rumors about the console’s features, like how it could have VR integration, for example, but we guess in a few months all should be revealed.