And Gaara himself owed a personal debt to Naruto for stopping him and making him see things clearly. Gaara was brought back to his senses after going on a rampage. Although they emerged victoriuos after a great loss, the Leaf village still let the Sand village off even after they had tried to destroy them, mostly because it had been Orochimaru who had been pulling the strings. The sand village's already financially weak state got worse when they realized that the Kazekage had been murdered and their team including their trump card, Gaara had been defeated.

He himself then posed as the Kazekage at the Chunin exams to successfully infiltrate the Leaf village. Orochimaru however, betrayed the fourth Kazekage and killed him. The Sand village was suffering badly economically and the Fourth Kazekage saw it as an opportunity to improve their economic condition by taking over the Hidden Leaf and also severely weakening the Leaf Shnobi forces, thereby naturally creating more opportunities for the Sand shinobi to get hired for missions. He managed to compel the Fourth Kazekage for assistance in destroying the hidden leaf. He continues his quest for immortality and wanted to destroy the village for his personal reasons. And it was him who put an end to his secret experiments back when he was still a leaf shinobi. Orochimaru obviously had a personal grudge against the Hidden Leaf village and the Third Hokage who was also his former mentor. If you haven't already gone through the whole arc, then these might be spoilers for you up ahead. But I believe it was because of the following reasons. It's been a while since I watched Naruto.

Village hidden in the sand