An inexpensive product performing almost identically to one many times its price is common in cosmetics and rare in most other categories. The structure of the industry makes it straightforward.
Formulas are largely unprotected
A cosmetic formula is very difficult to patent, since it usually combines known ingredients in known ways rather than inventing anything novel.
Regulation in most markets requires ingredients to be listed in descending order of concentration, which publishes a substantial part of the recipe on the packaging.
A competent formulator reading that list, with the product in hand for texture and performance, can approach it closely through iteration.
The same factories serve many brands
Most cosmetic brands do not manufacture. They commission from contract manufacturers who develop, produce and fill on their behalf.
Those manufacturers maintain libraries of base formulas that any client can commission with modifications to colour, fragrance and texture.
Two products at very different prices can therefore originate from the same facility and the same underlying base, differing in the adjustments requested.
Pigments are commodities
Colour in cosmetics comes from a regulated and finite list of permitted pigments, and every manufacturer buys from the same suppliers.
Matching a shade is a measurable exercise rather than a creative one, since colour can be read instrumentally and reproduced by adjusting proportions.
This is why shade matching is the easiest part of duplication and why dupes are most convincing in lipsticks, powders and eyeshadows.
Price separates on things other than formula
Packaging, in particular weighted metal components and complex closures, can account for a significant share of a premium product's cost.
Marketing, retail placement, sampling and the margin taken by a prestige retailer all sit on top, and none of them appear in the product itself.
Research investment is real at the premium end but concentrates in a small number of genuinely novel launches rather than across an entire range.
The genuine differences show up in specific places
Where premium formulas often do differ is in longevity, in the stability of the emulsion over time, and in preservative and fragrance systems chosen for tolerance.
Those attributes are the expensive part to develop and the hardest to detect at the point of purchase, which is why they survive duplication longest.
A dupe that matches on colour and texture may still differ on how it wears over eight hours, and that is the comparison worth making rather than the swatch.