Why must every Indian movie have a dance scene in it?

 Because Bollywood is Obsessed with peppy dance numbers and Indians want full entertainment for the amount they pay for the Movie. 

 There are various reasons for it.

1. Indians love music.
2. Dance scene makes the audiences glue to the theatres even if the movie has a bad script.
3. It's a formula used by the filmmakers to make a movie run for a while.
4. Iconic steps are created by Bollywood.
5. Dance is used to portray feelings of the character (in initial movies).
6. Dance scenes are used to attract audience.

My answer might not be Satisfactory but that's how Bollywood works..Bollywood needs dance because Indians carve for masala movies, a complete package like ala-carte package. All of the entertainment so Bollywood adds more dances and songs to the movies.Another reason is that most of the Indian audience don't like to think while watching a movie, so if the filmmakers put a song and a dance number they can relate to the audiences. If the actor is happy there'll be a dance party. If he wants to hook up he goes to the bar and another peppy party number comes in.Good movies in Bollywood does have songs but they are the demand of the script.Movies like The Lunch Box,Airlift,Neerja,Baby,Pink does not have dance sequences to convey their message to the audiences, because of the script..

Source: https://www.quora.com/Why-must-every-Indian-movie-have-a-dance-scene-in-it

If you are an indian reading this topic, I would love to hear your comment on this.