CY8C32xxx processors are based around the 8051 but they're actually part of the fairly capable Cypress PSoC 3 line[1]. The PSoC 3 includes an 8501 compatible processor along with a bunch of mixed signal peripherals and a PLD fabric to connect it all.

[1] https://www.cypress.com/products/psoc-3

And even a 7$/ku MCU is complete overkill (assuming that's the real price, not shortage-related, though its lead time is over a year, so the price is probably inflated), because literally any microcontroller with an ADC can easily do this. Around ten years ago I built my own on a tiny AVR, and even that would be an expensive option compared to what you could use instead in a commercial product (<0.5 $/ku ARM MCUs).

I haven't had a fan controller for many years though, because they're quite pointless if you do things right.

Still overkill. A 555IC, a variable resistor, a thermistor and a few passives is all you need. You could get the BOM for the whole #! down to under a buck.

Agreed but definitely must be quite a few orders of magnitude less crashes than a rPi for a fan controller.