Why are the "tributes" given stylists and dressed so elaborately for the opening ceremony?

The tributes are given stylists to make them popular. The tributes want to be 인기 among the people because then they may get sponsered to help them win the games. If a certain district's tribute wins the games, then they get glory and become 더 많이 popular. Also, the better a person looks, the 더 많이 appealing they are to the people.

The capitol wants people to be interested in the games so that the capitol can show how much power they have. It is all part of the Capitol's mind games.

I hope that helped:)
-Hannahleigh Em

To impress enough to gain sponsors. Besides, the people of Capitol nearly only cares about looks.

Remember that the Hunger Games is a show, the people of the capitol, and perhaps some from the districts, want to see a good show put on, they want to see who they will bet money for and who they want to sponser, looks play a big part in that.