Foundation settling into lines is the most common complaint about makeup on mature skin and it is almost always treated as a product problem — which leads to buying four foundations in a year while continuing to do the thing that caused it. The mechanism is straightforward and worth understanding, because three of the four fixes cost nothing.
A crease is a channel. Gravity and surface tension move any liquid on your face toward the lowest available point, which is the bottom of that channel. Once there, the water in the formula evaporates and the pigment stays — concentrated, and therefore darker than the skin either side. That is why a line looks more visible with foundation on it than bare, and why it gets worse through the day rather than better.
Three properties decide whether a formula resists this. The first is slip: how easily the product moves sideways across the surface. Silicones and oils give slip, and a product with slip crosses a channel rather than falling into it. The second is film flexibility: what the product does once the water has gone. A flexible film stretches when you smile; a rigid one cracks along the fold, and the crack then collects product. The third is quantity — the amount of material available to move in the first place.
Longwear matte foundations are engineered for the opposite of the first two. Their selling point is a hard, water-resistant, low-transfer film, and that is precisely what cracks. This is why the formulas marketed hardest on staying power are the ones that settle worst on a face that moves.
The fourth factor is not the product at all. It is how you moved it, and it is the one most people have never considered.