Chemicals are maybe the smallest cost of agriculture. Used to be > So saving even 95% is maybe not a compelling economical argument to use this.
Well not quite. resistance is a massive problem, so you need to spray more. But that kills off the soil, so you need to put more fertiliser in. But that means you get weeds, so you need to nuke the field, which means the soil blows away, which means you need more fertiliser....
Folks in the midwest largely use no-till single-application processes. Which prevents weeds from even starting.