Why do third party keyboards not support this feature?

I have used both SwiftKey and Swype and the single most annoying thing for me is that when you want to cancel an auto correct you have to erase and type again where as with the Google/AOSP keyboard all you have to do is press back space to cancel it and return to the word you actually typed. I mean this just seems like such an obvious feature why won't they include it? If someone is pressing back space after an auto correct then that just means they don't want the word to be auto corrected.

I am kinda surprised nobody talks about this.