Yes, this is crazy to me as well. I wonder if the reason you can't do it on your existing account is because of your license or some other factors. I'm adding my search query that helped me find this Community request, to hopefully help others. I hop...

This is absolutely incredible!  Strong work Airtable team!I have a question about using Cobuilder with existing bases.I have an existing base with the following tables:ObjectivesKey ResultsProjectsQuartersTasksSubtasksActivity & UpdatesI want to be ...