Note that this usage possibly developed from English speakers trying to avoid either "I" or "me" because they're not sure which is correct!
Young children will often use objective forms like "me", "us", "him" in a compound subject -- "Steve and me went to the playground", or "Her and Jennifer won't share their candy!" -- and then adults will correct them: "No, no, that's wrong -- you should say 'Steve and I went to the playground', and 'She and Jennifer won't share', etc."
So the kids develop a superstitious fear of the objective forms, and when they get older, they'll say things like "Would you like to have dinner with my wife and I?" And other adults may explain to them, in a polite whisper: "You mean 'dinner with my wife and me' -- because if you were to take out the words ...my wife and..., you'd say 'dinner with me', not 'dinner with I', right?"
And thus, having been corrected for using both "me" and "I", some people just make a habit of saying "myself" instead.