It was just called DHTML instead of javascript because:
1. Javascript was not nearly as popular as it is today.
2. DHTML actually supported multiple languages, it was a catch all term for any scripting that interfaced with HTML so it included VBScript, JScript/ECMAScript, ActiveX controls, etc.
It very much evolved into web apps as they are today.
(I don’t feel ActiveX, applets or Flash were ever part of the meaning of DHTML. JavaScript/JScript/VBScript, absolutely. But these others had their own drawing areas and typically didn’t interact with the HTML DOM. They were just embedded alternate worlds, not DHTML.)
For me the reason to include ActiveX is because it came bundled with the web browser (IE) while for Flash you had to install the Macromedia plugin. Also, while Flash probably could interact with the DOM I personally almost never saw it done; I definitely remember ActiveX controls that would interface with the DOM, used almost in the way React and co are these days (!)
No, DHTML meant little snippets that you could add to your page to add effects and widgets, whether arguably useful things like button rollover (many of you will remember the incantation I think it was Adobe Fireworks produced, something along the lines of <img src="button1.jpg" onmouseover="MM_something('button1_rollover.jpg')" onmouseout="MM_something('button1.jpg')">) or widgets like a “scroll to top” link in the bottom right corner that only appeared when you had scrolled down some way, or ridiculous things like drawing an analogue clock around the mouse cursor that followed your movement but as though the digits were connected by pieces of elastic each to the next, or snowflakes falling down the screen. Browse http://www.dynamicdrive.com/, that was DHTML. DHTML mostly meant fripperies, but did definitely include useful functionality like calendar widgets. But that was the scope of it: isolated things here and there that you could add to an existing page.
Web apps today are a whole-page affair, where the scripting is woven through the entire thing; they’re essentially unrecognisably different from DHTML.