We say "כל המרבה לספר ביציאת מצרים הרי זה משובח".
There are MANY mitzvos where "the more the better", such as tzdaka. So why only regarding Yetzias Mitzrayim do we find this phraseology of "the more you do it the more praiseworthy you are"??
Explained here.
Explained here.
