A CEO can only buy or move 20 corps to countries owned by the same entity.
After that you can IPO and buy shares in as many as the CEO can control.
Player countries the number is less unless, you gain them through the IPO of shares (which is surprisingly not all that difficult). There are a lot of players that don't want a ceo (probably because they lose free play).
And Khome, if they don't have the backup to control those corps themselves, it probably means they don't have the backup to move corps in fast enough. I can and have, pulled 38 (more but that's the most I've ever had to) fully upgraded corps out of a country in one game month.
Even with two CEO's they can't move them in fast enough and if they have to build we all know all corps suck when new and for a developed country the results are catastrophic.
Loss of employment, loss of income, totally porked
Yankee is the devil. El Diablo.
Being proactive, as in move in your own corps prior to another enterprise moving in. They can be declined also; don't accept too many corp offers from one CEO