a few things at play here - people talk about how no one young *not from a farming background* is getting into farming... that's the tragedy of the commons, isn't it. You need low barriers to entry yet the wise personal choice for landowners is sell for as high as possible. What is good for the individual is bad for the industry.
County zoning often disallows subdividing land into smaller chunks, so they often only come up in ~40 acre chunks. For a population that usually hates government intervention, most conservative boards of supervisors have zero problems with incredibly restrictive zoning laws. If you want new people in farming don' make them buy gigantic chunks of land.
There are several counties around here still with no zoning. They don't have any more new farmers than the others. This is an economy of scale problem and not attributable to zoning. A 20 acre plot won't make any money, unless you want to call like $5,000 / year a good salary for your hard work.