I'm extremely interested in this; how come none of the keyboards I've tried depart from the same layout as Apple? Is it strict adherence to guidelines rather than technical restriction then?
To wit, some of the features that same-named apps/keyboards give me on android but not on iPhone include "hold key for alternative character" or button to "force" numpad. As well all keyboards I've tried have same layout and sizing as the original one.
I assumed it was imposed on them in some way I guess?
I don't think there's much, if anything, in the way of App Store guidelines for keyboards except that they do things with the text field the user currently has highlighted.
For instance the app Fantastical comes with a "keyboard" that inputs dates that are open on your calendar[0] and there exist a few rather nonstandard keyboards like Typewise[1].
Absence of features common on Android boards I would guess comes down to those patterns not being familiar to (and thus, not desired by) iOS users or in some cases software patents (there have been a few cases of keyboard devs receiving cease and desist notices from patent holders for using some UI pattern).
To wit, some of the features that same-named apps/keyboards give me on android but not on iPhone include "hold key for alternative character" or button to "force" numpad. As well all keyboards I've tried have same layout and sizing as the original one.
I assumed it was imposed on them in some way I guess?