Blame schools of third world countries for this. In middle class "reputed" schools in India ( in one of which I did my education) , formal letter writing comes in annual English exam almost everytime from Grade 1 to grade 12 and every fucking single year they taught us to initiate formal writing with - Dear Sir or Respected Sir. I know this sucks, I never followed such bull shit guidelines and ended up getting a lot of marks "cut" because of frustrated teachers. The people you deal with - from India or similar countries don't think getting casual with you is a good idea and they believe " Dear Sir is the best way to address anyone for any formal purpose. Just my 2 Paise.