When I started, I found the world's content back then—which I noticed did improve here and there when I returned then saw new areas and quests—to be interesting enough for me to stick around. I grew up playing grindy games with harsh RNG for drops (and I also enjoyed Warframe), so I didn't mind that Nin required steadfast commitment to reach Lv50-60 as it felt very rewarding to gain levels, to get a rare item as a drop, and to learn new jutsus.
What made me stop playing was constantly being assailed by other players who were much higher level than me at the time. It made me feel helpless—like I couldn't get anything done until they left the area, and time is precious to some people depending on their lives/schedules. It felt even worse when you're unable to beseech those of your village to help you, but compared to the past, it has gotten much better in that regard.
While the grind from Lv1 to Lv50-60 can feel like a euphoric adventure at times during the beginning for some people like me, I will admit that it's... monotonous and very linear. We're killing the same NPCs for days—with only dailies, the few side-quests at certain levels, and leveling beyond those NPCs' level to break us away from that repetition, and once we are high enough level to move on to the next appropriate area, the repetition ensues.
Nin really could use dynamic content (e.g., #1 and #2) to artificially—this word isn't as bad as it sounds within this context—liven up its world, making it more reactive in response to its players, while providing new and interesting ways to earn XP and maybe even items/jutsus. We see this all the time in Naruto when the ninjas aren't focused on/distracted from the main plot (if the main plot isn't a source of their "distraction[s]" itself). Think of... Asheron's Call's live events—sort of, Guild Wars 2's dynamic events, meta events, and world bosses (best examples), and Elder Scrolls Online's world events.
I believe this would potentially rejuvenate the game, increase new and old player retention, and spread PvPlayers out from the spots where they would typically brutalize new/low level players.