Why do bankers tend to prioritize serving larger companies over smaller ones?

Its all about deposits. The money that large companies place as deposits is worth its weight in gold for many bankers.

One large corporation may decide to have US$ 1 Million in deposit (balance) at all times. Compare this to, for example smaller companies, which might have say $100,000 as deposits, in this example, 10 Small Companies = 1 Large Company.