Zelenskiy accuses Nato of lack of respect over Ukraine membership

I was wondering the same, does not apply to UK journalism style apparently

Use all capitals if an abbreviation is pronounced as the individual letters (an initialism): BBC, CEO, US, VAT, etc; if it is an acronym (pronounced as a word) spell out with initial capital, eg Nasa, Nato, Unicef

https://www.theguardian.com/guardian-observer-style-guide-a