Think about it. If there were, say, 8 people interviewed in the first round. After a week or so of organizing the interview schedule that takes 8 days to complete - and not necessarily consecutive. Then, say, you invite 3 back for a second interview. That's another 3 days plus organising. Then you have to agree on the final appointment - which takes a day or two. Then you have to negotiate the contract with the manager's agent - that takes another few days.
And that is assuming it all goes smoothly and nobody declines the offer.