why do あなた think princess 桃, ピーチ is the main princess?

Because she is pretty and girly and better than daisy

because 任天堂 made her before デイジー または rosalina and plus she the princess of the キノコ kingdom :)

because she has mario who rescues her about each day.

Because Shigeru Miyamoto created Princess 桃, ピーチ to be a part of the main cast.

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