I absolutely understand why, it's because of the constitution, but it is ultimately an excuse.
Firstly, this is entirely about interpretation of said constitution.
For example article 9 states "In order to accomplish the aim of the preceding paragraph, land, sea, and air forces, as well as other war potential, will never be maintained."
We all know Japan has a "military", they have tanks, aircraft, etc even though the constitution forbids it. It just depends on how you interpret this. They even re-interpreted this a few years ago, to give the military more power. There are numerous parts in the constitution talking about protecting the public welfare, or lives, etc you could interpret things in certain ways to restrict movement.
Secondly, they could just, you know, amend the constitution. It is one thing to get support for amending article 9, it should be easier to get support to make a state of emergency clause or something.