There's such an "ego load" associated with this investment too. I find that even when a developer comes to realise that the SPA mess is largely unjustified, they're rarely willing to admit or change anything.
Also bad is that junior engineers see shoddy client side code and internalize it. As an example, one junior engineer asked me how he was supposed to iterate over an array server side when I told him he didn't need to use Vue on a page. Server-side rendering fixtures had been completely forgotten.
I accept my responsibility in causing this mess though. I niavely pushed the SPA on my myself, my coworkers, and our end users years ago and have to live with that sin daily.