Sounds like you never worked on complex HTMX systems. They're easier to maintain, allow for easy caching of HTML fragments in a page. For higher traffic pages React just fails spectacularly.
Why would react fail for higher traffic pages?
If it's a traditional React SPA, you can use a versioned bundle with immutable caching and each user only has to download your bundle when you release an update or they use a new browser. You will need to think about how you handle spikes in traffic when you do a release, but even then users won't all load your page immediately after you bump the version.
Most of the time (existing user using the same browser, no update) there will be precisely zero traffic to your servers to load the React app except for the initial HTML skeleton.
For an app using SSR it's more complicated and I'll admit I don't know how that works at very high load
How does React fail for high traffic pages? It is amazing that you would suggest I don't understand HTMX "systems" and then go make such assertion.
I have been writing frontends since early 2000. So I have seen it all, from activex being shinny to jquery, mootools, backbonejs, angular 1.0, php, Java Spring, Go. I looked into htmx and it is very much a second attempt at angular 1.0, which I did use for some good half decade as that was the best option at the time, but sooner or later, you get sick of stuffing "little codelets" inside attributes all over the place, which is exactly what htmx does.
If you want to understand what htmx is going to look like at scale, look at angular 1.0 projects.