Where are the chocolate advent calendars???

I remember buying chocolate advent calendars well into December, including reduced prices after the 1st of December. I went to Sainsbury's, Tesco and M&S today - because I completely forgot to buy earlier - and they're all gone. Not available online either. I doubt they sold out yesterday, so why are they just gone? I've noticed this with lots of seasonal stuff, the day after they're "due", they disappear when, in the past, they'd be sold with reduced prices. It was such a good deal to get Christmas or Easter food cheaper after the date, now they're all full price until the last minute and no matter how big the stock is, in the next morning it's all gone. Seems like it's a massive waste as I doubt they'll end up in someone's house.