Candy companies don't run invisible psychological experiments on their customers. An app like Instagram is also self-replenishing, which can't be said for physical products with addictive qualities.
They do. Advertising is psychological manipulation (aka experiments).
There is no experiment happening once the candy bar is in your hands. The bar discloses its nutritional contents in a readable label as required by law. The same is not true of Instagram whixh is an algorithmic black box. The EULA is made intentionally unreadable and easily skippable, so its users ignore the risks.
They hold focus groups and push false narratives with popular characters.