The US soy bean industry isn’t one entity that can make a decision like that, it’s presumably thousands of discrete farms, each of which would have to pitch some in and then presumably endlessly bikeshed about precisely what needs to be done.

Coordination is hard. The overwhelming majority of traffic on the Mississippi is not soybeans. The soybean industry is not terribly concentrated. Why should they pay all the costs only to receive a small portion of the benefits? This kind of problem with large positive or negative externalities and myriad actors is usually the province of governments to solve. For another example see climate change.