Power consumption and cost. 10 years on a battery is very hard to achieve for microcontroller. https://sorwatch.net https://sorwatch.net shows that : with muc

Power consumption and cost. 10 years on a battery is very hard to achieve for microcontroller. https://sorwatch.net https://sorwatch.net shows that : with much more advanced microcontroller (much more modern tech.node, low power features) - it only works for 1-2 years on a single battery after extensive power optimizations. In custom silicon when seconds tick - it's maybe 100 transistors change their state. In microcontroller - it's roughly 10'000-100'000 transistors changing state to handle interrupt and update display content...