When I first published my app, they asked for a video of video fully working. Then once I had a bug and they sent me a video of it with the steps to the bug.
So there are definitely people opening and testing apps
Given the up-and-down, seemingly always controversial (and sometimes adversarial nature) of how Apple performs their app reviews and enforces their rules, I think it's 50% on lazy/bad reviewers and 50% poorly-communicated rules and regulations.
I wonder if there are a load of failed submissions too. They'd want to minimise effort so I guess they'd have good ways to quickly rebranding an app as a new one.
Or the app talks to a remote server so it works normally during the review period, but after the app gets approved the author changes a flag on the server and the app changes to "scam mode".