The reason you should do strength training

[PickMeDown]

Studies have shown that building muscle also helps to burn fat. Since your body needs calories to maintain the amount of muscles in your body, more muscles = more calories burned. The calories burn even while you are sleeping. I would say one of the best places to build muscle if you're trying to lose weight is the upper and lower back. Since they're one of the biggest muscles in your body they would give you the most benefits.
In short, if you want to lose weight more quickly incorporate some strength training into your workout routine instead of just cardio. You should be doing both.

 

[Mercury]

I would like to add that leg muscles also make up another huge proportion of your body's muscle composition. Legs and back combined easily makes up about 70% of the muscle mass in the body. So logically thinking you would be looking at spending 2/3 of your strength training on those areas.