As I understand it, the CRS trusts were a way of financing the purchase of the equipment. Rather than using the railroad's own capital to purchase the equipment, the trust bought the equipment and, in escense, leased it to the railroad. The railroad was responsible for making payments as well as maintaining the equipment. This is something like GMAC leasing cars.
To make a similar purchase using their own capital, the railroad would have had to find investors and sell stock, or create bonds. Instead, the trusts were formed by the principles of the railroad company, they raised the money for the new entity. I feel certain that there were tax benefits for doing this. In addition, the trust company was assured of getting paid. It probably provided a way for the owners to get paid first, no matter what other legal wrangling was going on.