I'm not saying people aren't still choosing Backbone/variants today, just that 2 years ago, Angular was (1) not a nearly as viable an option and (2) not nearly as well known; so any time /company-size correlation will push the results in one direction.

edit: although interestingly, looking at the respective wikipedia entries, AngularJS has an initial release listed in 2009, Backbone.js is listed as October, 2010