What's different about banks?

Negotiable certificates of deposit (CD's) trade in the capital market in competition with other securities like commercial paper and bankers' acceptances. If CD's must pay lenders competitive monetary interest, the reserve tax on CD's is borne by bank borrowers. Viability of the tax means there must be something special about bank loans that makes some borrowers willing to pay higher interest rates than those on other securities of equivalent risk. Moreover, there must be something special about banks that prevents other intermediaries from competing to assure that it never pays to finance loans with CD's.