The prediction of a crop failure isn't a binary event and money isn't deployed in a binary strategy. It becomes more or less likely over time.

Also, the situation is very dynamic with an unknown and very large number of variables, even with something as seemingly simple as a crop failure. Such as such as a countries deciding to ban exports to secure food security, lack of access to fertilizer due to sanctions against major fertilizer producers in wheat producing countries, the politics of national and local water rights.

All these factors have parties with inside information acting on them (see members of congress trading stocks) which no player with big pockets will have access to but is all reflected in the price.