I realise they don't use microcontrollers, but the Apollo Guidance Computer only had ~12,000 transistors[1].
The cheapest, smallest (15s storage) "chip corder" (which is what these cards use) has GPIO, SPI, the ability to trigger different messages etc. There's no way this is under 12,000 transistors![2]
[1] https://en.wikipedia.org/wiki/Transistor_count#Transistor_co...
[2] https://www.datasheets.com/en/part-details/isd2115ayyi-nuvot...
Music cards use dedicated chips, they are not general purpose, and they don’t really do much computation aside from a few counters. AFAIK.
Now, in DIY tutorials they show microcontrollers, because they are easier to obtain, but it doesn’t mean that they are used in the commercial products.