I disagree here. Of course alliances can be great debtors, but the implication that a bank can't survive without them is wrong. Nation loans can be quite lucrative if you do it right and efficiently.
You are right, lots of alliances offer interest free loans to members, but with proper sales work, there will be plenty of people looking to get loans. A majority of the player base isn't in an alliance with great lending power.
You may be joking in your first remark, but it is very possible to profit managing just a few hundred million in assets.
Going off of my previous point, there is profit to be made. And more importantly, smaller nations will grow and, if you cultivate a relationship with them, they come back to you with larger requests, meaning more profit for you. I've got a feeling you're trying to scare off someone from joining an already crowded market with these large numbers that are likely your own standard. Once again, in my experience, there is plenty of money to be made lending to individual nations in amounts ranging from just $20m and up, sometimes less. Surely, the more you loan, the more you make, but scale is a gradual process, not a gateway of entry.