[cge]

I had also heard a point for toothpaste involving the marketing: toothpaste advertisements, and all marketing imagery of toothpaste on a toothbrush, almost always show absurdly larger amounts of toothpaste than is effective or appropriate to use brushing teeth, trying to increase consumption by increasing waste.

[FridayoLeary]

Another explanation could be that advertisers are trying to increase the visibility of the product being sold.