Unions work best in industries that have captive audience, that's why public sector, and public-sector-adjacent (e.g. infrastructure construction) unions are the ones that stick around more; no matter how bad they are, the taxpayers can't choose to shop around. Stuff either becomes more expensive (infrastructure), or worse with consumers holding the bag (public schools; consumers do shop around, but it doesn't matter much to the unions because taxpayers still pay).

Or ports are a good non-public example, it's hard to "disrupt" a port. To the extent that industry is competitive, unions would basically destroy their companies... Big 3 automakers are a great example.