Guillermo Rauch is selling Vercel, whose strategy includes first-class tooling for SSR, convincing people to move their SPA to SSR, and then locking them in on their platform.
[1] https://rauchg.com/2014/7-principles-of-rich-web-application...
Referring to SPAs as a "zero-interest-rate phenomenon" implies that SSG/SSR models are more efficient in terms of financial cost of deployment. I don't agree this is necessarily the case, and I think SPAs can be developed and deployed sanely and cheaply also.
Vercel is doing some amazing things, but it's also innovating in ways that occasionally lead to "lock-in", in the sense that moving away from Vercel would involve a lot of friction. So I think it's fair to point out that you have a financial interest in convincing people to adopt delivery models that your business streamlines.
Longtime rails dev here. The reason smaller companies are using it is because you can move much faster working on a full stack rails app that gives you SPA-like functionality without needing to incur the performance or operational cost of a dedicated front end.
I've worked for both rails shops and JS shops, and the productivity achieved with Rails is staggering compared to React in a small team environment. Guillermo Rauch tweeted a few months back that SPAs were a zero interest-rate phenomenon and I completely agree. Just because a bunch of companies jumped on the JS hype train doesn't mean that they were all making the right decision.