Well I've had it happen with toilet seats. In 40 years on this planet I've only ever needed to purchase that one. I'd imagine if I needed to get more than one that I would get them all at the same time.
They’ve conflated “most purchases of a toilet seat are made by someone who buys another” and “most people who buy one toilet seat buy a second”.
There’s a small, but high volume group of toilet seat purchases — eg, office buildings or apartment maintenance.