You're conflating three different eras. There was an era where backlot filming was the norm ("classic" movies before roughly the 70s), an era where on location

You're conflating three different eras. There was an era where backlot filming was the norm ("classic" movies before roughly the 70s), an era where on location was expected by audiences (pre-CGI), and the modern one we expect now. That's all rough and the reality is more intricate.