Yes I don't understand why using a simple templating engine doesn't suffice.
I think it's a good idea. I have been writing vanilla JS for SSR'd pages for a while and inevitably reimplement some common patterns over and over (such as "load another page, select part of it, replace part of current page"), of which htmx looks to do a good job of capturing.
I completely agree. It's basically breathed new life into my job's antiquated .Net SSR [Razor] pages.
There is nothing HTMX is doing that I wasn't already able to accomplish with vanilla JS or Jquery, but holy shit has it reduced my need for either (which has also saved me time too).