Here's why:
* Sign language is a visual language with its own grammar, syntax, and vocabulary. It's not simply a translation of spoken language into hand gestures.
* The manual alphabet is used primarily for:
* Spelling names that don't have a sign
* Clarifying a sign that has multiple meanings
* Writing down words that are not signed
Think of the manual alphabet like the English alphabet. It's a tool for writing words, but it's not the language itself.
Deaf people use sign language for everyday communication, just like hearing people use spoken language. The manual alphabet is a helpful tool for specific situations, but it's not the language itself.