My in-laws do that with our daughter. I think they do it because they think it sounds posh (they're quite well-to-do Oxbridge folk). It really annoys me and my wife. But it really, REALLY annoys our daughter who always tries to correct them. She tells them off and they manage to say it properly a few times but quickly revert back to SharLOT. Ffs...it's not difficult. Even the BBC pronounce Princess Charlotte correctly.