Some ground isn’t suitable for much else than annual ryegrass, which does well on the clay mud in the hills and seasonal bogs. There’s not much to switch to that can even handle the conditions.
Other grass crops like different types of fescue are a multi year investments since the first year you don’t get much from the field and it takes time to clean up the weed seeds. So flipping to another crop puts you in a big hole.
Finally there’s the generally six figure equipment to harvest any particular crop. A given harvester can only deal with a very limited selection of crops, and even then is often going to require configuration and tuning when switching to a compatible crop.
I think the grape and hop guys might also be seeing something similar, but I’m not entirely sure.
I can imagine that growers with fields configured for growing rice face similar issues. If price tanks, they don’t have the flexibility to “just” pivot to something else as needed.
Japan is also a parliamentary system, and a significant portion of Single Member Seats in the House of Representatives are small towns or rural [0]
Pissed off farmers caused the LDP to lose power in the 2009 election [1], which is historic in a country that is a de facto one-party state.
The LDP in 2024 is looking similarly weak like the LDP in 2009 so they cannot afford to anger the farming bloc.
[0] - https://en.m.wikipedia.org/wiki/List_of_districts_of_the_Hou...
[1] - https://en.m.wikipedia.org/wiki/2009_Japanese_general_electi...