Why do text input methods generally omit an undo function?

I'm reading through my keyboard's resource documentation (I use [MessagEase](https://play.google.com/store/apps/details?id=com.exideas.mekb) normally), and I see that they state: > Please note the Android does not provide any **Undo**. However, I know this isn't actually true — at least, not in any apparent manner — because when using a **physical keyboard** Ctrl+Z invokes undo just fine, and doesn't require any additional/external applications, i.e., works natively via generic PNP (I've used telnet, BT, and RF varieties, all of which work). And yet, mysteriously enough, the function seems to be omitted *intentionally* (disclaimer: I have no evidence to support this conjecture). In fact, MessagEase has extended input functionalities that include form field controls and ASCII character controls, and yet inputting Ctrl+Z results in a notdef glyph output in the exact same form field. Why is this the case? EDIT: Please note that I am referring to connecting a physical keyboard to an Android device, I am *not* comparing PC vs Android UX.