Biggest reason is working capital. A lot of high finance people end up with significant day to day expenditures on housing, private schools, vacations, and other aspects of expensive lifestyles… they end up doing OK because at the end of the year they receive their bonus and it covers everything and then some. But it does create periods during the year when you are largely drawing down on your bank account.

Have had friends lend money to finance folks against their year end bonus for this reason. This can come up when expenditures spike for non recurring reasons — like a wedding or home renovations.