Why build your own instead of using the publisher bank
Publisher test banks are convenient, but they carry two real problems. First, the questions circulate. Answer keys for popular textbook banks show up on file-sharing sites, so a student who finds them has your whole exam. Second, the publisher bank rarely matches how you actually teach the course. You emphasize different objectives, skip some sections, and add your own examples that never appear in the shipped questions.
Building the bank from your own material fixes both. The questions come from the exact readings and notes your students used, so they test what you taught. And because the pool is yours and private, it is not sitting on a study site. You still get the speed of a ready pool. You just get one that fits your course and stays out of circulation.
The workflow scales down as well as up. A single instructor can build a bank one chapter at a time across a semester. A department can pool questions from several sections into one shared bank tagged by objective, then each instructor pulls their own version. Either way, the questions accumulate, and next year the hard part is already done. If a chapter is dense, generate from it in pieces and turn each reading into questions with the PDF to quiz converter before adding them to the bank.