[Stuart]

The official name remains the same because it's the long form name. A bit like how the official name of France is the French Republic, a lot of countries are like this. Introducing 'Czechia' is essentially correcting a long term error as almost all other languages already have shorter name for the country. It's still early days for the name and I'm sure it will grow in popularity as it becomes more normal.

Lest we forget FYROM/FYR Macedonia/North Macedonia...

Macedonia is an entirely different situation where you had a country and a neighbouring Greek region claiming to be called Macedonia. It lasted for many years until 2019.

Nobody else is claiming to be called the Czech Republic. It's the name of the country, there is no 'long term error' as far as the people of the that country are concerned.