That's three full routines you didn't buy because the money was already spent.
Nobody buys a product intending to abandon it. It happens for a few specific, predictable reasons — and once you can name them, you can see them coming at the till.
Skin reacts to a bad week, you buy something for it, the week passes, the product doesn't fit your normal routine. Buying in response to a temporary state is the single most common source of shelf clutter.
Sets are designed so that one product you want carries four you didn't choose. The per-item price looks great and the abandonment rate on the extras is enormous.
Not enough to return it, enough to reach past it every morning. A small texture irritation is the most reliable predictor of a half-used bottle there is — and it's exactly what you can't judge from a photo online.
Boring and almost entirely effective. One cleanser at a time, one moisturizer at a time. It forces you to actually find out whether something works, and it removes the option of quietly abandoning things.
Products bought as a set of choices you made — for one budget, one routine, one purpose — get used. Products bought individually on separate impulses compete with each other on your shelf.
The goal isn't to spend less, exactly. It's to finish what you buy. A $50 routine you use to the bottom is worth more than a $200 shelf you use a third of.