But can they not just house a computer inside? A lot of modern modules _do_ just have a computer inside - for an open-source example, many of the Mutable Instr

But can they not just house a computer inside? A lot of modern modules _do_ just have a computer inside - for an open-source example, many of the Mutable Instruments modules use AVR or STM32 controllers: https://github.com/pichenettes/eurorack https://github.com/pichenettes/eurorack