I heard it was because Apple’s C-levels weren’t happy with any of the concepts for a calculator UX that fills the screen of an iPad - and they’re right, even the best iPad calculator there is (PCalc) feels weird to use just to do some quick sums because it fills up my 13-inch iPad Pro’s screen.
I remember some early fan-made concepts for the iPad had it running iPhone apps in floating windows - I think if Apple baked that functionality into the iPad OS from the beginning it would have meant a whole slew of small utility apps like the calculator, clocks and alarms, compass, etc wouldn’t need to be remade - but I’m sure they killed that idea because it wouldn’t motivate developers into making first-class iPad apps - and by “punishing” users with the terrible full-screen iPhone app mode it incentivises developers to put effort into making good native iPad apps - while at the same time making small utility apps an impossibility for iPad OS (though this doesn’t seem to have convinced Instagram...)
To be fair, they could exist now as a Today Screen widget, but then you can’t use it while you have another app open. It’s only with iOS 12+ multitasking support for slide-over and side-bar apps that a calculator app could now work - but it would still need to support full-screen mode - but we’re so close now! And given that, I wouldn’t be surprised if Apple did allow iPad apps to run only in sidebar or floating mode - but only if an app really won’t work as a full-screen app - and when/if they do, they’ll definitely launch their own calculator app.
Y’know the Apple Watch didn’t get a first-party calculator until 2019?
Apple believes it should make/provide the whole “widget”. If they think every phone should ship with a really good weather app, they’ll do one. If one comes on the market that they think is better, they’ll buy it and make it the new default.
I mean they’re not in the weather app business. They aren’t competing against Dark Sky. What they’re competing against is Android, and if their phone comes with a stellar weather app out of the box, that is good for Apple. Others can continue to make weather apps.
iOS comes with a calculator. People still buy PC Calc and Calcbot despite the built-in being pretty useful.