I mean it's an interesting idea, but it's weird to imagine that small time farmers in poor countries are capable of obtaining and using a sickle but are somehow not capable of obtaining and using a scythe. At least looking for ones here in the US, a decent quality sickle seems to run in the $30-$60 range while places that sell scythes seem to cost $100-$300, so I can't imagine it's some massive price barrier either
Taking inspiration from your nickname, how do you explain the many technical aspects of Japan that are still stuck in the 90s? They surely know how to look around and they surely know better things have been battle tested for decades in other countries, and yet...
Old people don't like to adopt new technology or ideas
Countries with demographic cliffs likely also try to extract more labor out of older people. So decision makers for adoption of new technology and techniques which would go with management or some other analogue, have reduced neuroplasticity and won't adopt change as readily.