A small amount of high-grade bonds with low default risks are transacted at organized exchanges. Organized exchanges usually impose a volume limit on corporate bond transaction. Large volume is all done through OTC. Take the U.S. market, a highly developed bond market, as an example. Institutional investors hold about 90% of outstanding bond and individual investors hold the balance.
He must always be ready to meet his liabilities at all times. In case of a banker not able to honour his commitment, he will not only suffer a shock of such a failure, but the shock will also be transmitted to the rest of the economy very quickly. The systemic risks arising from that need to be eliminated or minimized.