You still quite easily can if you own the land outright, even in the grain business. The problem is that you need multi-millions to buy 100-200 acres, which nobody wanting to start farming has, save situations of inheritance. That means, for most, the vast majority of the potential profit turns into servicing debt or paying rent to the actual landowner. When you are only receiving a small portion of the pie that the land is actually generating, that's when you need thousands of acres to accumulate enough.

To put it another way: The going rate for rent for farmland around here is around $300/acre. $300 * 200 acres = $60,000. If you own the land and don't have to pay rent, that alone is a decent living; more than most people make. And that is ignoring the profit that someone renting would expect to make off the land.