I use Backbone because I see it as the C of javascript "frameworks". It doesn't do anything, it doesn't pretend to be all-encompassing but it's small and efficient. The fact that it's been in use for quite some years also created an ecosystem of good practices and additional software to complement what some people consider shortcomings of Backbone itself. But shout out to all the other frameworks who are tackling the problem from different angles and provide choice and competition to the field, this is all very healthy and will make developers and ultimately users happiers in the end.