AngularJS, Angular, React, Vue, Svelte. That's 5 in 11 years. I could add Knockout, Backbone, Meteor and Ember. That's 9 if you're stretching it. I don't know anything about the last 4, but the first 5 ones all offer different ways to do things. I would even argue that they are more different that the "canonical implementation of the backend MVC framework" and the "Sinatra copy" that you have in every language.