The smaller leg muscles, we can pick on the extensor digitorum longus or the sartorius (as examples) are not supposed to be individually engaged. They are role-specific, and supposed to serve in a helper capacity.
A good overview of skeletal muscle functioning could help explain a bit, but realize that some muscles are purely antagonists in their role, resisting the force of the larger and more powerful muscle (the agonist). As such training them directly isn't going to be as useful as training them to as proportionately strong as their full power neighbors.
A good example of the interconnected web of muscles would be the tibialis anterior (shin muscle), which largely serves as an antagonist to the peroneus longus (popped out upper calf area), which serves as an antagonist to the peroneus tertius (down near your ankle).
Even if you could target those muscles in isolation (which you can't) how could you possibly keep track of how strong they are? They're designed to be proportionate to one another. Making an antagonist much stronger than its agonist is not a good thing.
If we're talking about bridge construction, you want the suspension cables strong enough to keep the bridge up, not under such tension that they rip the bridge in half: if you want to bring more tension and power to the suspension cables you need to strengthen what they're pulling on (the lateral aspect of the bridge).
Properly performed compound lower body exercises (like a clean) will activate your muscles and connective tissues in the way they were designed. Your primary movers will do the heavy work, and the synergists and antagonists will do their thing, all in balance.
Keeping with the example of the power clean, look at the articulations listed (like ankle plantar flexion) and note the muscles engaged: all the little ones along with the big ones.