Who knows.... Actually, if other international markets had it a few months after it was released, then why didn't the US? That does not make sense. The first Godzilla movie was released in the US about a yr after it was released in Japan after filming scenes with Perry Mason (can not remember the actors name) himself in it for the American audience.
If I were to hazard a guess it would Blu-ray rights since they are often a big mess. Since Japan and the US are the same BD region and the US sells media like BD, DVD, CDs, etc. for much cheaper than the Japanese market, some Japanese consumers will import American versions to save money. In order to counter this, the Japanese are often stricter with giving out BD rights or stipulate, as a condition of the contract, long waiting periods before said show or movie may be released on BD by the rights holder in the states here.