Because ng-repeat does create a new child scope(prototypically inherited) on each iteration when it repeats a template on wherever ng-repeat directive has been placed.
So what happens when ng-repeat creates a new prototypically inherited child scope?
In the child scope it carries all properties in which primitive
property initial value taken while creating child scope & object
values are taken with their references so update in parent scope value
will update in child scope value & vice versa.
Here in your case you had ng-model="kindSelected" variable inside ng-repeat so that scope variable got create inside the ng-repeat scope and doesn't available outside ng-repeat directive.
To fix such a problem you could use object while defining ng-model so that you could follow Dot rule while defining ng-model. That means you could define a object called as $scope.model inside controller & then add kindSelected property so that the value will get updated on selection of checkbox.
Markup
<div ng-repeat="kind in movieKinds">
<input type="radio" name="movies" ng-value="kind" ng-model="kindSelected"> {{kind.name}}<br>
</div>
Selected Movie :{{model.kindSelected}}
Code
$scope.model = {};
The other way to fix this problem is to use controllerAs syntax which will use alias of controller so the scope hierarchy related problem doesn't happen on HTML. Whichever controller variable you want you could use that alias of the controller.
