Strength training is not cardio/aerobics
The mistake people make when doing this is believing they are going to get greater fat burning with the goal of trying to see how tired, sweaty and winded they get during a workout and judging their strength training workout by how many calories they burned.
This is a very flawed way to train. It takes away from the goal and reason you are strength training which is to try build muscle and gain strength. This is what makes strength training the greatest type of exercise to sculpt your body (build muscle and lose body fat).
This is not to say that you can’t ever cater a strength training towards a fat burning goal at times. Many a good strength training workouts such as lactic acid training, German body comp, etc can produce very good fat loss results but these would never be confused with a cardio/aerobic workout and not the type of workouts I see people do in some of these boot camp/group fitness classes which seem to have the goal of just getting people exhausted and with the feeling they worked out hard.
A good strength training workout should be structured, progressive in nature and with the goal of getting you stronger and building more muscle over time.