Why do people consider dogs loyal?

i know dogs are branded as the most loyal pet ever but why?i'm just wondering because i cannot get a thought of how they can be "loyal".i mean,other pets would be "loyal" too,right?rabbits,cats,hamsters,you name it. But what separates dogs from a lot of them?
Update: excuse me,dark wolf,but are you saying that the other animals i've mentioned are dim-witted?!that's not nice.there are birds far more intelligent than some dogs
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