> Surely it can't be a mere lack of land that drives the cost of rice.

It's not, it's a consequence of some land reform policies that made sense after WW2 to take power away from the rich, but has meant that economies of scale for rice farming has suffered later on.

The median rice farm owner in Japan only is in charge of single digit acres, whereas in EU/US it's like tens or hundreds of acres. So it's harder to justify mechanisation since the economies of scale don't work out and the children of farmers don't want to continue working the farm after their parents are no longer able to because the ceiling of what the farm can produce is low and economic and social prospects are better elsewhere.

That's without even getting in to the JA and the fact that a lot of these farmers are part time.

It's a really complicated issue without a simple fix or cause like labour costs. Realistically these farms are going to have to get consolidated, which is something that is happening, but slowly.