RY: I’m gonna assume you didn’t fully read (comprehend) what I wrote. So let me repeat.
A time of Bar/Bas Mitzvah is cause for great celebration. And we try to portray ourselves, as excited and wiling to take on HaShem’s mitzvohs now as “metzuvah v’oseh”. The more “dagesh” the better, it shows our goal in life, what’s important to us.
But a girl’s innate tznius precludes this, her entrance into a world of Mitzvohs should be in a tznua’dig fashion. So they do have enthusiasm, it’s just from the inside – ???? ??? ?? ??????.
ps as an aside, there’s a most beautiful song for a Bas Mitzvah, starts with something like “Come my dear daughter.. Today is the day..”