Why did WHO skip 2 letters in Greek alphabet & name the new COVID variant Omicron?

WHO has named the new COVID-19 variant Omicron. The variants are named after Greek letters, but while naming Omicron, experts skipped two letters Nu and Xi. "A WHO source confirmed [they]...had been deliberately avoided. Nu [was] skipped to avoid confusion with..."new" and Xi [was] skipped to "avoid stigmatising a region", they said," tweeted senior editor of The Telegraph, Paul Nuki.