Probably because they don't want people talking cross-purposes or confusing their proposals with what is implemented in other languages, as they call out in the intro:

"As the term generic is widely used in the Go community, we will use it below as a shorthand to mean a function or type that takes type parameters. Don't confuse the term generic as used in this design with the same term in other languages like C++, C#, Java, or Rust; they have similarities but are not the same."