Every time you hire someone, you train them from the beginning, with whoever happens to be free. Each person passes on a slightly different version, shortcuts included. Six months on, you have four ways of doing one job and you can’t tell which one lost that customer.
You’ve thought about writing it down. Probably on a Sunday. You opened a blank document, got as far as “Step 1” and realised you’d need three weeks you don’t have, and that half of what you do, you’ve never had to explain.
That is the actual job of an SOP consultant. SOP writing is the easy part. Getting the knowledge out of people’s heads, agreeing what the right way is, and getting people to use it afterwards: that’s the work.