Why do things in two places when you can do it all in one place? This isn't limited to computers, but unless you are getting specific benefits, it isn't wise to continue with a SPA approach.
We had the same and worse problems with "thick clients" that came before the web grew. With the right requirements, team, tools etc., you could sometimes build great apps. This was incredibly difficult and the number of great apps was relatively small. Building with earlier server-side web tech, like PHP, isolated everything on the server and it was easier to iterate well than with the "thick clients" model.
SPA reinvents "thick clients" to some degree and brings back many of the complications. No one should claim you can't build a great SPA, or that they have few advantages, but the probability of achieving success is frequently lower. Frameworks try to mitigate these concerns, but you are still only moving a closing some of the gaps and the probability of failure remains higher. Depending on the app you can move the success metrics, but we often end up fudging on items like performance.
We get to a point where there is current model is fraying and energy builds to replace it with something else. We end up going back to old techniques, but occasionally we learn from what was done before.
I find that it's surprisingly rare for people with 1-2 years of experience to be able to give an accurate overview of the last 10 years of web development. A better understanding of this history can help with avoiding (or targeting) problems old timers have encountered and complain about in comments.