Food is pretty localised for those without good storage means, if the local food supply reduces then prices rise. If there's less food than there was before, and people want the same amount then prices will inflate and overtake the extra income. Those not growing cash crop will fall behind, leading to pressure to stop growing food ... the local community needs food growing but the market won't price it properly. Whilst food is most vital the other crop can be sold in wealthier countries.

People grow coffee and chocolate whilst their countries suffer famines. People sell water rights to multinationals whilst their countries suffer droughts ...