Some people want to do the bare minimum to get by and eat convenience foods rather than changing their habits to embrace healthier, less processed foods. If you take a quality multi and eat whole foods, you will gain much more energy than eating a highly processed diet and taking fat burners.
What's worse, the jitters you get from the energy tablets are negative side effects. Your adrenaline system is being stressed. Stress creates cortisol and this inhibits fat loss. So you might feel more energetic, but your body is actually in a state of stress and may not be as capable of burning fat as the marketing hype would have you believe.
Finally, your body does adapt to the energy burners. If you continue to take them, you can suffer from over training and fatigue from the over stimulation of your parasympathetic nervous system. If you cycle off of them then you simply lose the energy kick you were receiving and reintroduce the negative side effects when you cycle back on.