I think the reason for such 'restriction' was due to the inhibitive placements leveled on Japan by our American partners after the war. Do you know that in the Japanese constitution (which was written by American military men immediately after the war) had specifically placed that Japan would be "unallowed" to develop export-focused military material, or Japan should be directed not to export military material as it would be "contrary" to the Japanese alliance with America. lol.
Trust me, i'm no America-hater, i respect America (heck i live and work here), but at the same time the restrictions that America had leveled on Japan truly inhibited Japan on the production level and up to the policy level.
It was only recently , my friend
@Bornubus , the summer of 2015 to be exact, that under Prime Minister Shinzo Abe -- Japan had removed that clause in the Japanese constitution that had strictly forbidden Japanese military exportation (they placed that clause in the constitution to begin with). After that was done, Abe then also removed the clause in our constitution that had forbidden Japan to wage war on a defensive scale. The next goal is to totally re-write the Japanese constitution , and the goal is to have this realized by the 2017 time frame.
We have Obama to thank for this, of course. And hopefully when Clinton wins in 2016, we can expect to see a totally revitalized Japan, one that can take part in global military arms trade and development --- competitively.
Sadly there is truth to this, thanks in part to US restrictive policies in Japan. In fact the restrictive policies America had leveled on Japan is FAR MORE restrictive that what she had leveled on Germany and/or Italy, lol.
It is as if America does not trust Japan. I don't understand why, really.
But , we have to make due with this reality. Work on what we have, work on even with American 'concern'.