In the end of Harry Potter and the Philosopher's Stone, Voldemort commands Quirrell to seize Harry.
Harry sprang toward the flame door, but Voldemort screamed "SEIZE HIM!" and the next second, Harry felt Quirrell's hand close on his wrist. At once, a needle-sharp pain seared across Harry's scar; his head felt as though it was about to split in two; he yelled, struggling with all his might, and to his surprise, Quirrell let go of him.
"Seize him! SEIZE HIM!" shrieked Voldemort again, and Quirrell lunged, knocking Harry clean off his feet' landing on top of him, both hands around Harry's neck -- Harry's scar was almost blinding him with pain, yet he could see Quirrell howling in agony.
"Master, I cannot hold him -- my hands -- my hands!" And Quirrell, though pinning Harry to the ground with his knees, let go of his neck and stared, bewildered, at his own palms -- Harry could see they looked burned, raw, red, and shiny.
Previously, Quirrell had bound Harry with ropes.
Quirrell snapped his fingers. Ropes sprang out of thin air and wrapped themselves tightly around Harry.
Why didn't Quirrell do the same when he was commanded to by Voldemort? Even if it hadn't occurred to him, why didn't he do so after he realized he could not touch Harry with his bare hands? He could then search Harry for the Philosopher's Stone without having gone through all the trouble. Considering how much wizarding adults rely on their wands (or at least on some form of magic) to do their tasks, it seems illogical for Quirrell to physically dive to seize Harry, when he would be able to keep him still with one snap of his fingers.
My question is: