The first is size itself. Without the guarantee that one’s personal assets are off limits in a lawsuit, one must take more risk in buying stock in a corporation. Imagine if potential stockholders knew that their personal assets might be at risk in a case like the BP oil spill. Some number of shareholders would decide against taking that risk, or at least limit it by acquiring less stock.
If Obama tried abolishing limited liability corporations and give trial lawyers who win a case the ability to take the CEO's mansion he would be called a communist and be impeached by the end of the day.