For any market to gather huge volumes and carry out its function of enabling efficient price discovery, the critical factor is the presence of entities with deep pockets which can act as market makers and provide necessary funding support when required.
Banks running large proprietary books with the backing of huge balance sheets carry out this  BIS central bankers’ speeches  3  function in the institutional markets. Banks remain the ultimate warehouses of liquidity and provide easy and convenient access to liquidity in times of need.