Several of those are going to be perennial and end up competing with mono-culture crops the following year(s) (not that I'm trying to defend mono-culture crops, but that's what they're planting). It's a good idea, but not necessarily as simple as you're implying. Still it's an idea that's not without some merit. The biggest obstacle to adoption is no one is making a significant profit off of it, so it's unlikely to see much uptake.