Fingertips don't reach the scalp properly, especially through thicker hair. Silicone nubs work shampoo down to the skin and lift the buildup that causes flaking. Also feels good, which is why people keep using it.

Increased blood flow to the scalp is the other argument for it - the evidence there is thinner, but the cleaning benefit is real either way.

Works shampoo down to the scalp

Lifts buildup that causes flaking

Soft silicone, won't scratch

Grippy handle, works with wet hands