7-9 rounds just means 7-9 conversations. Just talking to a recruiter and the manager are 2 rounds. So 5-7 interviews that evaluate competency. You usually get the lower end unless you ended up giving mixed signals.
Sounds like asking a lot from candidates but unfortunately candidates lie a lot and the cost of hiring candidates that don’t match up to the requirements when paying $300k-$500k/year is just too high. Firing people is hard and takes a long time, especially in management roles. My personal guidance to managers is to have rounds match the level and experience required for the job. You can hire an intern with 2 rounds after the hiring manager conversation but a staff IC probably needs 5, directors need 7.
It's an effect of "once burned twice shy". Every time there was a "bad" hire they had to change things. People add to the list but no one ever wants to advocate for a lighter process since they might be blamed for it.
IME (hiring, not interviewing) it's always been 3-4 rounds. First is an HR phone screen (usually 20-30 minutes on the phone), 2nd with hiring manager, 3rd with a senior engineer/architect, and a 4th with the hiring VP. And those are almost always combined into a single morning or afternoon(2+3 or 3+4) and the final round doesn't always happen (VP's choice).
I'd say it's more incompetence than cruelty. People (edit: I mean companies) have options and don't know how to filter, so they just go nuts in the worst possible way.
These companies have lost their minds.