Most true small businesses can't exist in markets with a lot of competition. Highly competitive markets have a lot of fluctuation and businesses with little capital fold when there's a downturn.

In fact, most markets naturally go from high competition to monopoly or oligopoly. You can see this in chips, cars, airplanes, steel, ecommerce(Amazon) and beyond. Indeed, many oligopoly situations only fail to be monopolies through either antitrust activity or through nation-states supporting their competitors (chips).

Agriculture in particular tends to be geographically dispersed so it's harder to have absolute monopolies. But some "harking back" claim of "if we only had small business, all the predatory stuff wouldn't happen" really fails to understand the dynamics of markets. Scale in agricultural production is what allows the low prices you get in stores - But $10 cage-free organic eggs are available at my local coop for those who love small businesses (though I prefer the $2 cage free eggs at nearby Grocery Outlet).