The IOU Variant would've been too obvious.

First reports of the Omicron variant were originally calling it the Nu Variant. So the name could change.

Nu and Xi names were skipped. MSM says Nu sounded to much like New. And Xi is a common name (would probably remind ppl of China where the whole mess started).

https://www.businessinsider.com/omicron-variant-nu-because-it-sounds-like-new-2021-11

The IOU Variant would've been too obvious