Travel Stack Exchange uses exclusively English as a language of communication, so all proper names are translated to English where possible, and the native spelling provided where necessary. When there are alternative names, the most common variants are preferred, for purely practical purpose -- facilitating external and internal search, primarily. In this particular case, using Czechia as an alternative name has a very limited appeal -- the official name of the country in English is Czech Republic, and Czechia, while it can be easily inferred which country it refers to, is just not known among speakers of English. The missing definite article is easily added, and you can suggest an edit to the post and it will surely be approved by a moderator or a high-rep user.
For another example, the name of my country is България, but can you tell off-hand which country it refers to? How many other users can? I don't think using this name exclusively is useful to people from 中国, ประเทศไทย or قطر trying to find information about it in English.