why do 당신 think princess 복숭아 is the main princess?

Because she is pretty and girly and better than daisy

because 닌텐도 made her before 데이지 또는 rosalina and plus she the princess of the 버섯 kingdom :)

because she has mario who rescues her about each day.

Because Shigeru Miyamoto created Princess 복숭아 to be a part of the main cast.

데이지 doesn't get the same luxury because Super Mario Land was made without Miyamoto's knowledge. (Or so I was told.)