In the absence of a third-party with IP rights on seed, dominating corn growing means you dominate the seed supply and have the most variety to select from for improved traits (whether yield, hardiness to particular environmental stresses, etc.)
Seems to have a pretty clear feedback loop where dominance breeds dominance in the same way as with network effects. Sure, the source of the feedback loop is different, but it's very much there.
How did Google displace previous search engines?