Reasons Why Microsoft did not include all the Keywords.
To Understand why Microsoft did not include all the Keywords:
1- PORTABILITY:
Microsoft intends to make VBScript available on a variety of platforms, including Windows, Mac, Unix and so on.
2-PERFORMANCE:
Speed of features, Microsoft removed many non-esential features from VBScript so scripts load and run faster.
3-SAFETY:
You should be concerned with security on the Internet.
You don't want to open a Web page and discover that it contains script that
crashes your hard drive.
Microsoft removed any Visual Basic feature that might cause a security problem
with the script such as file I/O.