On Shabbat and Yom Tov Ashkenazim say an extended kedusha in musaf (on Yom Kippur, we even say it throughout the day). The Artscroll (machzor, Yom Kippur, pages 406-407) explains:
During Mussaf of the Sabbath and of Festivals, when we recall the additional Teple offering that symbolized the higher level of holiness that we were privileged to enjoy, we are permitted to combine our own tribute with that of the angels.
[that "combining" constitutes the expanded kedusha according to the notes, citing Chullin 91b]
But on Rosh Chodesh and on Chol Hamoed, we also have a musaf service which recalls additional offerings. Why wouldn't we say the expanded kedusha then as well? Are these offerings less indicative of a particular level of holiness? The musaf davening on Chol Hamoed is the same as for Yom Tov (aside from the specific offerings listed), and Rosh Chodesh as a time for atonement, seems more akin to Rosh Hashana and Yom Kippur, so we should be elevated then also.
Is there another distinction which explains the selective use of the expanded kedusha so the issue of extra offerings is not the decisor?