1. Tooling, yeah, you gotta have node installed, but that's pretty much the last time you have to touch it. I'm not anti-node or anti-js by any means, but the tooling around them often turns me off. Getting to do front-end work without _having_ to think about 'em is a breath of fresh air.
2. Less duplication of effort. I don't need to define schemas twice... once in the "backend" and once in the "frontend" application. You don't think this is bad until you spend two hours adding a adding, removing, or changing a simple property to your application because you have to update the backend, the backend's api docs, its tests. Then on the frontend, adjust the schema, adjust the frontend tests, and finally see if it's working.
3. Faster iteration. I prepare a new context, and can immediately consume it in a view. Views are reloaded instantly when changes are made during development reducing the time it takes to get feedback and increasing how fast I get shit done. Also less duplication of effort REALLY helps here...
4. We (at least me) got S(F)PA idea totally fucking backwards. The idea isn't to make you're entire web site a Single Fucking Page Application, but to make individual (single) pages which NEED TO function like applications do so... Quintessential examples that do _NOT_ need an SPA: a fucking FAQ, about, or contact pages. In fact, having an "application" on top of them is more burden than not.
5. CSS is really powerful these days and provides a lot of what the 2008-2012 JS movement was trying to do. If I combine that, with being able to re-render only part of the page, I've got almost the entire flexibility of what SPAs offer with almost none of the complexity.
6. Going to a new page, and causing a page refresh, but totally knowing the next page isn't going to be broken because of the previous page's state. Page refreshes are awesome. Growing up on 28.8k that wasn't the case, but ever since I got above 10Mbps its really not something I ever even notice (though I do notice when pages are broken that shouldn't be because they're SPAs and not just fucking content).
I could probably keep rambling but I'll stop here...
For point #2, it gets even worse if you're doing GraphQL. Another layer of data abstraction on the backend to update and worry about and another layer on the frontend as well (using Apollo, etc)
What about LiveView/Phoenix made the process more enjoyable - let's call it 'less painful'?