The only real consequence of a debt spiral is the loss of the black market and the decreased share price, neither of which seem to matter too much in the end-game
You're kidding, right? A handful of well placed mutinies on offworlds have won me soooo many games. Look at match 2 of my series against Heisenberg. Black market won that game for me, hands down. Why do you think Scavenger is so strong in the current meta? If black market isn't deciding your late games then you need to practice using it better.
Plus debt growth is exponential. When you hit that critical 20%/30% interest tick range it will CRUSH your stock price very quickly. Debt matters if you let it get out of control. The goal is to keep it on a tight leash just short of game ending.
That's on top of that what Yerand said. Right now debt is in a nice place where it's something to be balanced rather than feared. Your change would make debt something universally bad, and that doesn't make for a very good game.