yom tov - Why skip Yikum Purkan and Mi Sheberach on a weekday Yom Tov?

This is a question specific to Ashkenazim (Nusach Ashkenaz, Nusach Ari, and Nusach Sefard).

On Shabbat, after the Torah Reading and before Mussaf, 3 prayers, (2 Yikkum Purkans and a Mi Sheberach) are recited. On Yom Tov that falls out on a weekday, we are instructed to skip those prayers.

Why skip Yikum Purkan and the Mi Sheberach for the congregation on a holiday that falls out on a weekday?

There doesn't appear to be any Shabbat specific text, so why omit it?