They never left. But SPA is now more in demand than the old school server-side rendering where you return HTML in your response and let the web browser render it as is.
Decoupling back-end logic from front-end logic has just too much positivise and advantages that doing SSR is just so 2000s. JS brought dynamicity into web page rendering a long time ago. With SPA, or maybe even PWA(who really uses these?), you get also decoupling from the server - a data dynamicity, so to speak.
In short, SPA turns a dumb web page into a dynamic and responsive application that can have the look and feel of a desktop program. Web is no longer static and slow but fast and lively.
Nowadays, static HTML is a niche use case for serving web pages. Like a personal blog or corporate website that is static in nature(information there change sparsely) and can be manually typed or compiled via static website builder, like Hugo.