For one thing it got on toonami while Bleach went to adult swim and One Piece went to 4 kids. Meaning it was able to corner the American and therefore the international market. Since, in theory, Bleach was only seen by teenagers and adult. While One Piece was edited to make it 'kid friendly.'
Also, Naruto was a lot more engaging and draw viewers attention much quicker and keep them invested more than One Piece or Bleach did early on. One Piece was a slow build.
It didn't really have much competition on toonami. So, it quickly became its best and biggest show for years becoming the next Dragonball in the US.
It had decent action and morals to keep people interested in the story.
But most importantly the characters were likable and relatable enough that viewers got invested in the characters.
The reasons for its decline was people knew the giant filler arc was coming and lost interest. The problem was toonami was already in the red so when enough people stop watching Naruto filler arc it went down. It moved to Disney XD (cause disney thought it would be a money maker) which most people didn't watch before it was shuffled back to toonami/adultswim. During this people just started watching the anime online then reading the manga online.
People also didn't want to be associated with the weeboos, and the crazy obsessive toxic nH/SS pairing fans. So, if they continued to watch/read Naruto they did so in private. Since, those two group were so bad most anime fans turned their nose up at it. Also, most anime fans consider Naruto too well know and popular and would rather watch and discuss lesser known more obscurer anime so they could more elite about themselves compared to those peasants in the Naruto fanbase.
Also the editors constantly changing after the pein arc, the war arc itself, SP going all out with their desire to make Hinata Naruto's love interest at all cost, and general mismanagement as well as a decline in quality in both the manga and the anime.