Here's why:
* Proper nouns are specific names (people, places, organizations, etc.). They don't follow standard spelling rules and are often unique.
* Spell check focuses on common words and their correct spellings according to dictionaries.
* There are too many proper nouns to be included in a standard spell check dictionary.
However, some advanced spell checkers or grammar checkers might have:
* Custom dictionaries: You can add proper nouns relevant to your writing.
* Contextual analysis: They might recognize certain proper nouns based on the surrounding text.
It's still important to be mindful of proper nouns and double-check their spellings manually.