What's the reason why English and most other languages of Europe treat blue and green like distinct basic colors, while many languages of Asia have one word encompassing both? What's the reason why Hungarian has two basic words for different kinds of red? It's just a historical artifact of language evolution. Russian happened to the evolve two different distinct basic color words for blue; to an English speaker, both are different shades of blue, but in Russian, neither is a shade of the other; and Russian has no single color word encompassing the English concept of "blue".

Two basic color words for different types of blue. You might think of azure, cobalt, and sapphire as shades of blue. To a Russian speaker, синий and голубой are not shades of each other, they are different basic colors, like blue and green in English. And there is no one color word in Russian encompassing all blues.