They have gone publicly on record saying they didn’t find an “Appley” way to bring calculator to the iPad. As an iPad user myself who has used 3rd party calculator apps this whole time, I get it. They all suck. The interfaces are all over the place. It is enough for Apple to let users download whichever app best fit their needs, instead of staking their claim, as they do with all their other apps, that the calculator app they made is the best one.