This leaves me with two main cons to the idea:
1. Some people don't want foreigners in their country. I think their reasons are legitimate, but hear me out. Let me break it down into two categories:
Big nations: Well, since they are big nations, those second teams wouldn't be that impactful anyway. It would take those managers a long time to build up their teams, from bottom to top divisions. Some would reach top divisions after a while, but rarely.
Micronations: Maybe some micronation managers like to beat bots and pile up cash, but they will probably get bored after a while, and would welcome some human competition.
2. It will be harder for lower league teams to improve, foreigners stand in their way. Ok, you don't want 300 new mangers joining your leagues. So, what would you do if 300 new people from your country signed up?? I think the fear of competition is the main factor here. But let's say you have it your way, and you start promoting, by your country userbase declining. Let's say eventually, you reach the top division simply because your competition is leaving the game, one by one. I can tell you, you wouldn't feel any kind of succes and accomplishment, beating bots would bore you out quickly. And this is not hypothetical blabbering, you can ask the micronation managers, some posted here, they all say they welcome the competition.