Making the class add 2 methods and a field for every place the interface would define a field adds noise. And if you have a class with 20 interfaces, that can be a lot of noise. When you consider that the class itself doesn't actually need to know anything about the field because only the interface uses them, it's just... ugly.
That's more of an issue with Java not having properties as first class language feature. In C#, you don't have to deal with fields at all, because auto-properties do all the same things:
