Both 613 Jewish and 7 Noahides are called Mitzvos (ז' מצוות בני נוח)
We have a separate Mitzvah for every Ervah (one for mother and one for sister etc), for a total of 22 (I think).
Non-Jews have one Mitzvah that includes 6 Arayos (Rambam Milchamot 9)
"שֵׁשׁ עֲרָיוֹת אֲסוּרוֹת עַל בְּנֵי נֹחַ. הָאֵם. וְאֵשֶׁת הָאָב. וְאֵשֶׁת אִישׁ. וַאֲחוֹתוֹ מֵאִמּוֹ. וְזָכוּר. וּבְהֵמָה."
Why in Judaism each one is a separate Mitzvah and for NJ they are just details of one Issur?