It is, though. It's not an independent state, but it absolutely is a country. The two are not synonymous: for example, the United Kingdom is a single state, composed of three countries (England, Scotland, and Wales), part of one (northern Ireland), and perhaps numerous others as well (depending on how you classify Cornwall, which has a distinct identity and history from the rest of England, and the many many smaller islands).
It is only a historical country! The politic division of the Czech Republic is very different from the United Kingdom. Země Česká https://cs.wikipedia.org/wiki/Zem%C4%9B_%C4%8Cesk%C3%A1 was abolished in 1948. Since that time Czechoslovakia and the Czech republic was divided into much smaller districts (kraje and okresy).