* The backing of the largest web company in the world.
or
* Inclusion in the second-most popular browser in the world.
Yep. That aught to do it.
VBScript had both (actually the browser was the most popular), and look how far it went.
it only worked in IE and Windows.
True, but times were different. Microsoft was being evil in the browser wars, being a monopolist and pissing off the hacker community: just the people you need for a new tech like this to take off.
One can also argue that VBScript is not tooling-friendly. I am talking a little out of school, since I have never had to use VB.net; it could be wholly different. But I have had my fair share of VBScript interactions and those were not fun (Microsoft-isms aside).
VBScript was one of the most popular server-side scripting languages in the late 90s. If they had a JavaScript translator, MS developers would have used it.