[userbinator]

At these sizes, the packaging is probably a significant fraction of the cost. They may also offer a bare die version at < $0.01 each.

Despite its name, this is not an 8051. Looks like this competes with the PIC10F200 which costs dozens of times more yet has a similar "RISC" (that's what they call it, but it's more like an 8-bit accumulator architecture) ISA and general layout.

[nine_k]

Packaging is always a significant fraction of the cost. It can be 20-30% for a typical MCU part, and nearly half of the cost for a complex chiplet-based CPU (where the internal assembly is indeed complex). I suspect that manufacturer's profit margins are lower than that, especially for simpler MCU parts.