I think you might be missing something. If food yields were soaring that would decrease the market value of food. The current agriculture system is designed with profit as the goal and feeding people as a secondary result.
Is a supply chain inefficient? In the current system that's alright, it lets a company charge more to make up for losses and gives them something tangible to justify price hikes.
There's also massive surplus waste and other problems that are prevalent in the current system. Growing to feed local populations rather than growing for export would drastically shift the situation alone and is currently entirely possible, but not nearly as profitable.
Can we get enough food for everyone? Yes. Can we do it while maintaining record high margins? Probably not
They aren't concerned primarily with employing people or crop yields, agribusiness is a business.
Your sentiment holds entirely if agriculture was entirely dependant on staple crops.
The plateau didn't come out of nowhere. Staple crops are being pushed aside in favor of high margin crops for biofuel and luxury goods. Large agriculture still focuses on short term gains.
Profit per acre is going up. Businesses don't care about increasing yield past a certain extent. If the business is set to profit and is currently profitable then all of these issues are non issues to the business.