If you don't need a rest API, all it does is make everything far more complicated, i.e. every page now has two end-points, one for the html, one for the data.

It's trivial in most web frameworks to have an endpoint respond in two ways, one with all the html including head, menus, footers, etc. if you hit it with a GET, the other just the snippet if you hit it with an Ajax request.

A REST API is basically a massive over-complication unless you actually need it for a good reason, say you're running both a web app and a mobile app from it.

I've used this technique occasionally for over a decade and personally have always found this server-side approach very simple compared to juggling REST APIs with client-side rendering when a client or an existing code base demanded it.

I've also always found the defence 'you might need to switch' to be a flimsy one. Usually when you do need to switch, everything is so different even your 'future-proof' API design needs a massive overhaul too because you made assumptions you didn't even realize you were making.

Think of all those SOAP or XML APIs that were future proof...