Having just learned that in Old English the word for was written as fore, why is therefore still written as it is currently, and not as therefor?
Being a non-native English speaker, many times I automatically write therefor, as my brain probably is thinking on for. Alternatively, many times I also write fore, as my brain is probably thinking on therefore.
Edit: the possible duplicate is about the difference between the two expressions, and it would only be relevant if the actual reason why it is therefore instead of therefor is to distinguish them. But since that is not the reason, I believe that question is not a duplicate of this.