Htmx is a direct descendant of Intercooler.js, which has been around since circa 2013, more than a decade. Intercooler still exists and is used in production, and you can clearly see that it works almost exactly the same way as htmx does today, it just bundles jQuery together.
The creator has been working on these ideas for a long time, but the core idea–swapping HTML from the server into the DOM–has been constant throughout.
It's exactly because he followed the past two decades of web dev that htmx avoids almost everything about it. Fixi and htmx extensions follow the 80/20 principle and can work by just being dropped in with a script tag. You don't need an elaborate npm setup, same as everything else in the htmx ecosystem.