In their defense, plain 70s attire isn't really a common style of fashion anymore* where rocker/metalhead is pretty common (even if people go all out at shows).

Sounds like this artist has encouraged 70s vintage fashion or advertised a 70s show specifically. Still doesn't make every show a costume party for hecks sake 😂, what a silly idea

* In no way means to imply there's no one out there doing it