Language in the title is bait, let's get that out there right away.
It is true that for a significant amount of cases where you see SPAs used, HTMX could easily replace whole framework, leading to a simpler project, but maintaining the snappy, responsive experience we know from SPAs.
I've had the pleasure of working with htmx in some recent projects, and indeed it removes any need for a front end SPA.
It's basically a rather expressive jQuery, especially when mixed with hyperscript.
A lot of times we implement a SPA just because we need an interactive experience and we don't want to write jQuery and keep track of state in a weird way.
htmx+hyperscript gets rid of that need. The interactivity and state tracking can be done with the back end. In the end you have a situation where the source of truth, the back end, is also the one that gets to dictate what gets rendered.
Overall it leads to a much simpler application.
Of course if you have the real need for a VERY interactive experience, difficult application-wide state tracking, then a SPA is the correct solution.
If you just need some interactivity while developing your app, a SPA is overkill and overcomplicated.