Why did override and final end being identifiers with special meaning instead of reserved keywords?

Both the override specifier and final specifier were added in C++11. They differ from other specifiers added such as constexpr and decltype in that they are not keywords and are available for use as identifiers:

int main()
{
  int override = 0 ;    // Ok
  int final = 0 ;       // Ok
  //int constexpr = 0 ; // Error
}

They are what is referred to as identifiers with special meaning, which is covered in the draft C++11 standard section 2.11 [lex.name] (emphasis mine):

The identifiers in Table 3 have a special meaning when appearing in a certain context. When referred to in the grammar, these identifiers are used explicitly rather than using the identifier grammar production. any ambiguity as to whether a given identifier has a special meaning is resolved to interpret the token as a regular identifier.

and Table 3 -- Identifiers with special meaning lists both override and final.

Why did these two specifiers end up being identifiers with special meaning instead of keywords?