"feel like a single-page app" except that its not and it will never be. I hate HTML-over-the-wire solutions to any problem. There is not a worse solution that has been more normalized than html-over-the-wire.
That said, the vast majority of websites are purely transactional: click a link, load a page; submit a form, load a page. For those, there's little reason to add a full frontend framework. HTML-over-the-wire can improve responsiveness without adding complexity.
I have been extremely bearish on html-over-the-wire solutions from the minute I saw and understood what HTMX was trying to achieve. In my eyes, the only way to truly achieve what I, and users, expect in a web page is with a SPA. I understand the hesitation to use heavier SPAs, but my hesitation to fetching html from the server after the page load to update the page is much larger. But I also do understand how html-over-the-wire provides a good middle ground between web 1.0 apps where basically every interaction reloaded the entire page, and web 2.0 apps that feel closer to an actual application rather than a website.
Hypermedia libraries like htmx etc. are just doing these interactions, the ones that need a server request-response cycle. The difference is they get the response as already-rendered HTML, so they don't need to do anything further, just swap it in to the existing page. It's super simple and very efficient. And usually results in fewer AJAX calls which also are much more minimal and don't include any redundant data.