"It's a universal framework based on Vue.js" - from docs (nuxtjs.org).
So, I personally speaking the main purpose of the born of this framework is to solve one big issue that facing every developer or optimizer people.
Let's call server-side rendering (SSR).
SSR is a technique of creating a view on the side of the server, so that browser that requests to our sites will receive a response in the form of HTML.
In the short explanations, SSR will affect to "Search Engine Optimization", we usually say SEO.
SEO is highly important for our site performance because search engines likes google will do the crawling process (to find our sites depending on an HTML page).
The goal is to be indexed by a search engine, so that our sites will increase in every aspect (visitors, performance, optimization).
So, here we go!
Nuxtjs come and solved that issue!