I think SPA is just one of results created by libraries/frameworks like React, Vue,.... Those things were created not to produce SPA (we can do with vanilla JS)

I think SPA is just one of results created by libraries/frameworks like React, Vue,.... Those things were created not to produce SPA (we can do with vanilla JS), it's for modularization and componentation. Or we can say, they are implementations on how to achieve the same thing. The difference is performance.