It turns out, before 2020 the cereal industry was seeing a decline in sales. However, once the pandemic really hit the US last March, sales starting spiking for many brands. Obviously a great thing for many of them... except Grape Nuts. Because they were trending down, it was a shock for them to see a spike in demand and, unfortunately, they couldn't meet the need. If you've been looking for Grape Nuts on shelves, don't worry; they'll be back in March.
Between the GameStop Stock Market fiasco and now this, 2021 is teaching us about the economy in the weirdest possible way.
This article from Bloomberg breaks down the nitty gritty of the cereal numbers.