My take on debt is debt accumulated in 2 ways:
1. Life support required - The reason for life support drawing on debt opposed to cash is that it can be difficult to have the cash available to fix the issues which are accruing more debt. If the shortage is large due to high cost life support and it drew from cash on hand first, the cash would be drained before you can purchase another claim or building to correct the issue. If the cash wasn't allowed to remain, the player would end up in a debt spiral.
2. Auctions - The reason auctions draw from cash is that it presents a fairer auction method than just who has the most cash on hand automatically winning the options. If a crucial auction comes up, players can spend their future cash/resources to obtain the crucial auction.
Everything else draws from cash or requires cash to purchase. There is an option to have tighter debt rules than can be enabled which draws from cash first, but I find that annoying. .
I think that the developers have chosen to not allow more freedom obtaining debt is because it creates some weird situations. For example, If I could freely borrow money, early game would be completely different. I would just borrow as much money as reasonable possible and stock up on necessary resources (glass/electronics) while they are cheap, and it would be a question of who could hoard faster. It would also allow for buying up the last bit of stock at no risk because you could just assume as much debt as necessary to buy someone out with no risk because the game would be over. Neither really enhance the game experience. So, restricting the acquisition of debt to the above 2 things, the gameplay experience is more stable.
