why do you think princess pêssego is the main princess?

Because she is pretty and girly and better than daisy

because nintendo made her before margarida or rosalina and plus she the princess of the cogumelo kingdom :)

because she has mario who rescues her about each day.

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

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