It's easy forget these days, but Windows had this thing called Active Scripting, that was basically a set of COM-based interfaces for scripting languages to expose their functionality OS-wide, and for apps to use any scripting language available on the system. And Internet Explorer, at the peak of its popularity, used that interface to implement the <script> tag - so long as the user had some language installed on their machine, it could be used to script web pages in IE. Active Scripting came with JavaScript and VBScript supported out of the box, which is why both were available in IE. But there were quite a few third-party ones - I recall seeing Perl, Python, Tcl, and REXX.

But, of course, other browsers didn't have that. And even at the time when some websites really only cared about IE, they couldn't assume that people had any third-party runtimes installed - so you very occasionally saw VBScript, but pretty never anything else.