
I hate piling up a lot of cash because the return on cash is deeply negative given inflation. If you have a lot of debt outstanding, you can deploy cash to pay back the bank, which provides a pretty decent savings.
Later in the game I pursue huge debt financed acquisitions, which is a real hassle because you have to buy a lot of shares from your subsidiary. This infuses a huge amount of cash into the sub, which never knows what to do with it. The bank won't grant you incremental borrowing capacity to complete a merger because it doesn't realize you access a huge amount of cash when the merger is completed. Consequently, sometimes I wind up having to issue shares to the target company

My suggestions/thoughts:
The AI should use a significant amount of debt when it makes sense for it do so. Debt financing in the game is incredibly attractive. Sometimes you even get negative real interest rates on a floating rate loan, which is basically free money. The problem with doing this is that the AI public float would disappear even more quickly than it does already. One of the things that annoys me already is that private shareholders wind up owning so much equity over time. I think the player and the AI should have a lot less money at the beginning of the game. Maybe this is already something I can change. I'm not too up on the modding options.
Maybe some kind of bridge loan feature. May be too hard to implement.
Maybe some kind of risk premium on debt when you get closer to your borrowing limit. This would make taking on massive leverage less appealing.
I'm not sure what the borrowing limit is based on. It definitely takes into account asset value (fluctuates a lot if you have a lot of stock). Since stocks are very volatile, if you have a big stock portfolio it can swing dramatically. It might be good for the bank to give you less credit for volatile assets (in this case pretty much just stocks).
Maybe interest rates should just be higher relative to inflation. The return on capital is so high early in the game that its very hard for debt financing to bring down your ROE if you're allocating capital reasonably well.
If the bank could somehow call your loan after a period of time (revolving credit agreements in real life obviously require periodic extension or refi,) that would be a huge reason to pare back leverage. That's probably too hard to implement, however.