If you are not in that part of the legal business which involves representing Banks on lending matters, you may not know that Banks love trust deposits. They pay a ridiculously low amount of interest on them, and while the firm’s mixed trust account (the “General Trust Account”) requires some managing, it does not take much effort to service the individual interest-bearing investment accounts for specific clients (the “Individual Accounts”). It is good business to have.
On the other hand, law firms like bank lending work. Less now than back in the days when it was more profitable, but still.