Why does the interbank market exist?

Because the supply of Eurodollars is lower than the supply of dollars in the US.

Because the interbank market helps domestic banks to access international financial markets

Because the demand for Eurodollars is higher than the demand for dollars in the US.

Because some banks have surplus of Eurodollars, and some banks have deficit of Eurodollars, and interbank loans move surplus of money to feed the deficit.