That is true. Union shops are not as ubiquitous as they should be. They are in major cities or they exist in cities with arenas or conference centers ( although that is not always IATSE but can be other unions like IBEW) but there are a ton of LORT theaters that are around the country which will have Actor’s Equity but not IATSE.

Summer stock is also kind of it’s own thing. Where I worked in college at The Lost Colony on the Outer Banks the only Union jobs were the principal Actors. Everyone else were basically non union college kids and locals.