By intentionally introducing a long artificial delay.

They pick a date several weeks after shipping that every store is likely to have recieved stock and be ready. Stores receive stock in the meantime but are forbidden to sell it.

They don't tell consumers when they've shipped it and many retailers could have physically sold the device days, if not weeks, before the 'launch' date. .. if it weren't for the manufacturer forcing them to not give their customers what they want.