Keep in mind that Busicom was pretty much asking for a custom made controller in the beginning (more accurately, a set of chios), but Intel suggested a simpler

Keep in mind that Busicom was pretty much asking for a custom made controller in the beginning (more accurately, a set of chios), but Intel suggested a simpler solution. In the end, calculators ended up being sold in such large volumes that it ended up being cheaper to have an application specific controller. (That said, more sophisticated calculators still use microcontrollers.)