Why are they know suggesting resistence training more than cardio for weight loss?

ever since i could remember, cardio has always been the thing that people said to do to lose weight. even whn u go to the gym, most people are running or on the elliptical. now it seems that people are saying building muscle and resistance training is key. what really helps wtih weight loss and how much. i am sure it is a combination of both. please help. i want to understant what works and apply it to get results! i have 50 lbs to lose. of course i am also working on my diet, but that is for another question. here i am want to learn bout excersise.