For most commercial clients the fee schedule is only half the price. The other half is the earnings credit their balances generate, and for a large operating account it can outweigh the fees entirely.
At most institutions that half is run somewhere else. Fees are billed in one system, earnings credit is calculated in an analysis package or a spreadsheet, and the ECR a relationship manager negotiated is applied by hand to the accounts someone remembers are covered.
The gaps show up on the statement. A rate concession that should have ended keeps running. A client on a negotiated rate is analysed at the standard one and their treasurer finds it before you do. And when a correction is needed, the old statement is regenerated, so nobody can show what the client was actually sent.