Maybe you are in a hurry.
Perhaps you are trying to tell a joke.
Is it possible that you are having a bad day?
None of these things matter to the person on the receiving end of your emails. When communicating by email people can’t hear your or see your face so you have to be extremely careful in the way you word things.
I try to always keep a smile on my face when I type emails (especially if I am upset) but sometimes that doesn’t cut it and I have to be reminded …