Can't think of a good reason Sony might control stocks or shipments of PS5 but possible reasons might be
1. They want to spread out the financials so that the big numbers from PS5 sales don't get squeezed into certain quarters eg. usually 4Q or 1Q of a previous and next calendar years, numbers are very good due to holiday/festive spending but middle of the year is much slower
2. BOM cost contracts, big squeeze from suppliers of parts, they're hoping to sign better deals for future/larger contracts to get better pricing
3. Stockpiling to time more PS5s release into sales channels during major A-list game title releases
4. they look at the PS5 platform as money maker over longer term, eg. 6 - 8 years with gradual increase in profitability as yields and part supplies improve, so it's not really an advantage to sell so many initially where the margins are poor or even negative
5. They want to sell enough to sell more games as this is where the real money is made. But if installed base is small, game sales will also not be as large so it's also not good to release too many A-list titles during the early part of a console's launch when installed based hasn't reached a certain number. But it's also the games that sell the console.....hmmm
Any other thoughts? Interesting to think about how this biz works lol