Because I have enough money to travel the world to take magnet measurements.
You never take vacations? Brah, I think it's about time then I reveal this
get-rich-quick scheme for you. I 100% guarantee you LOTS of money.
Prove the world is flat, and 1.000.000$ would be NOTHING compared to all the money you would make by discovering, with definitive proof, that the Earth was flat, and then writing a book (or several) about it and the huge conspiracy, getting nobel prizes, getting movies made about this/you and getting royalties, getting interviews, become world-famous, making expeditions, selling merchandise etc etc etc etc
(in before "noone would believe just ONE person, no matter how good his proof is - not even ONE out of all the 6 billion people on this planet would check if his story was true, after seeing proper evidence. Even though this would be one of the biggest discoveries in the whole world.")