Many times when companies have a big sale it’s not uncommon that they will only put X amount of products for the public to buy and once they are sold out they simply tell customers that they have no more. Usually in those cases there are tons of the same products laying somewhere in the warehouse for example.
That’s usually why too if I am ever trying to snag a very good deal and it appears to be sold out I usually check on the last day of the sale or so. Reason being is that I usually find that people from companies accidentally replenish the stock thinking that the sale is over or that there are miscommunication such as someone new starting a shift and not being aware that they sold all the company wanted to at the discounted price.
As well too, a lot of people sometimes hold stock until the very last day to try and spread out the sale if the item seems to be selling a lot. I just got a deal that way today for example where I wanted to buy a 32GB micro SD card for my new phone which I saw for $40 before and it was sold out. Not surprisingly, on the last day of the sale today there were suddenly some available for sale.
Don’t expect this to happen if it is genuinely a brand new item that just hit the market. But for more generally stocked items it’s something to keep in mind if you were debating about just settling for something else thinking that the item will be sold out by the time the sale ends.