This is a 50 billion dollar (or yen equivalent) public relations exercise. The government wants to look like it is actually doing something about an issue it has zero control over now.
The Japanese government doesn't want to admit the truth that these areas are going to remain uninhabitable for hundreds, if not, thousands of years - because it promised the Japanese people that they would be able to return to their homes. The technology doesn't exist to clean up all this contaminated land. TEPCO continues to cover up how bad the situation is at the plant, just like they did from day 0 of the disaster.... and the mass media in Japan continues to sweep all the depressing problems under the carpet and out of view of the public as if the nuclear contamination can be cleaned up with a big enough vacuum cleaner and enough time.
They don't want to admit the ugly truth, and want to keep perpetuating this lie that people will be able to safely return to their homes..... one day.
If they ever return, they'll all get higher risk of cancers and the government and TEPCO will disavow that the reactors had anything to do with it because they "decontaminated" the area.... most likely. Just an excuse to try and dodge legal culpability.