Suggestion: Single Page application architecture issue

I have written a web app (Single Page application) which has only frontend technologies involved (Vuejs) and when I compile it, it will ultimately generate web pages (only HTML and JS). I can run this app anywhere by opening the index page.I am consuming REST API powered by oAuth on this SPA (making direct Ajax call to REST API endpoints).

But the problem is, My lead developer is saying the SPA must be powered by back-end service (Server) for example nodejs, apache. And the backend should make call to the REST APIs not directly Ajax calls from the browser (Frontend JS ajax). My SPA app runs anywhere and works perfectly on browsers even without any server.

My question is, do I really need to render and run my SPA using webserver, whats the reasons behind making my SPA (Plain html, js) app server powered??

Also please suggest me, if people simply write app using JS and HTML (pure front end) and upload on the server and point a domain name to that html-js web app which will be consuming remote REST APIs.

Thank you for making my doubts clear in advance.

I have remote REST API provider, suggest me best way to write an SPA to consume that remote APIs.