Why do they move? Africa
Africa is experiencing this migration two ways. In Ethiopia Indian and Saudi entrepreneurs leasing land for industrial farming displace people. In Zimbabwe industrial farms have been seized for Africans lacking money and skill. They always produced less from more ground. Now they're moving on too.
Many leases for African ground are signed over to ag businesses from Saudi and India. Almost any crop growth in Saudi requires expensive irrigation, and Indian farms are crowded and overworked (but practices can still be improved).
And yes Ethiopia is the same place that is in the news because drought has driven many people off the land, but it's not all that way. Even in Sudan, where the plight of Darfur is in the news, not all land is unworkable. Much can be done with it.
The big issues:
1. In the short term, factory farming will increase the food supply, but how long will it be sustainable.
2. Industrial farming has to supply food to non-growers. Some of them are the "huddled masses" crowding into cities. How can they "pay" for it?