A longer propeller with higher pitch generates more lift at a given RPM, and thus also generates more drag. Because it generates more drag, you need more power. More power in motors comes from higher wattage and higher efficiency. For a given efficiency (not all motors are equal) a higher amperage and/or a higher voltage will generate higher wattage, and thus higher power.
So, it's not that higher length/pitch "generates" higher power, it's that they "demand" higher power.
I think Hobby Lobby is bad for many reasons. I'd rather buy from A1 Main Hobbies, or HobbyPartz, or (worst case) Hobby King. Those stores all have various motor/propeller combinations, forums, videos, and tutorials.