He's lived a long time at this point, long enough to see the end of Hyrule, and just wants this accursed conflict to be over with he's tired of this ceaseless struggle. His willingness to hold back during his battles with Link and Tetra (Zelda) was probably a sign of him getting fed up with his destiny. But Because Destiny Says So, Demise's hatred for the goddess and her hero caused him to seek out the Triforce for these ideals, twisting his noble desire into a thirst for power. Think about it chances are, Ganondorf most likely would have just been a Gerudo desperate enough for his people to survive the harsh desert winds to try and make a complaint to the King of Hyrule at the time, probably come to an agreement, and that would have been the end of it.