#2. The potion probably took time to make in any case. Polyjuice potion takes a long time to make -- just imagine how much 'bring me back to life' potion takes to make.
#3. Voldemort was planning on returning that night using that very portkey to get into Hogwarts. It makes for a better return to show up at the tri-wizard tournament, rather than show up in the middle of Gryffindor Tower.
#4. Harry Potter and the Pillow of Doom would be a very short book.
If Colin Creevy, who is a year younger than Harry is his biggest fanboy, wouldn't the French girls who were 2-3 years older than Harry at the time know about him. Hell, you'd think plenty of girls who aren't muggleborn or Slytherin would want him.
It's the same reason Hermoine picks Ron. The same reason something happens to turn everyone against Harry even though he should be worshiped as a God. Same reason Bella Swan is designed to be average. It's so the majority of people can place themselves in their shoes and relate. In actuality, Harry would bang out every girl in school and his ego would become more massive with each one.
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Realo won gold at the Sex Olympics with a BROKEN FRIGGIN NECK.-Voltch