Ichigo Kurosaki is the protagonist of the Bleach anime. At first, he was designed as an everyman hero to whom readers could easily relate. Ichigo started off strongly in the Bleach story, but his appeal arguably wore off -- he soon became distinguished only for his combat skills rather than his personal journey.
It's true that Ichigo has some sympathetic traits, and his personal arc included moments of heartbreak, tragedy, triumph and more that defined him. As a whole, though, he doesn't compare well to other shonen heroes such as Izuku Midoriya, Monkey D. Luffy or Naruto Uzumaki on a personal level. Why is this?
A Sympathetic Lead, Then A Battle Scene Enabler
When Ichigo was first introduced, he was clearly the newest incarnation of Yusuke Uramaeshi, himself a great role model for how a shonen hero should be. Ichigo was tough and aloof but also kind and compassionate. He would risk any odds to protect his friends and family and stand up to bullies or other antagonists. Ichigo became Chad's best friend when he helped fight off some aggressive bullies, and Ichigo also had a happy boyhood where he was completely attached to his mother, Masaki. Tragedy struck when the Hollow called Grand Fisher killed Masaki, who had lost her Quincy powers, and Ichigo faced her murderer years later as a rookie Soul Reaper with a generic Zanpakuto.
His fight against Grand Fisher was personal, and it was heartbreaking when he failed to slay that Hollow. A little later, Ichigo was horrified when Rukia was dragged back to the Soul Society to answer for her crimes, embarking on a pseudo-isekai adventure into the Society to save her. That is noble and admirable, but by the time Ulquiorra Cifer abducted Orihime and took her to Las Noches, Ichigo embarked on the exact same quest once again. He wanted to rescue Orihime and keep his friends safe, but that was a given, and fans needed something more. At this point in the story, though, Ichigo didn't have much left to offer on a personal level. This isn't to say that he became a terrible protagonist -- rather, he became a bit tedious as his character growth hit an early plateau, despite later revelations such as his Quincy heritage.
By this point, Ichigo operated as the story's vehicle for exciting combat scenes, but he did little more. At first, he was the gritty underdog with a tragic history to add more layers onto his basic role in the Bleach story, but all that was phased out as Ichigo slew his personal demons and became an unstoppable powerhouse. That, combined with his circular goal of "protect my friends from the newest enemies to show up," made him quickly grow stale.
Ichigo Does Not Dream Big Like Other Shonen Leads
What does Ichigo dream of? Not much, it seems. His primary motivation in Bleach is to fight and defend his friends, which is noble, but that's not enough to sustain an entire character arc from beginning to end. In fiction and real-life alike, the most successful people are often those who set lofty but attainable goals and systematically pursue them. In this department, Ichigo lags far behind the likes of Naruto, Luffy, and Izuku. Ichigo is not aiming to become the world's protector or a great leader or even a role model for anyone else. He only reacts to danger and new enemies to shield his friends from harm, meaning that on his own, Ichigo isn't trying to accomplish much of anything. He has no inner goal, dream or motivation to move his character arc or the overall story along. Instead, he prefers a quiet and ordinary life, and that's not much of a goal for the sake of entertaining fiction.
In-universe, no one can blame Ichigo for pursuing a normal life and not living on the edge every day for the sake of it. But still, this may make Ichigo a less compelling and sympathetic lead in the Bleach story. Other shonen leads are relatable because they are gritty underdogs who spend the entire story trying to achieve their big dreams. Naruto Uzumaki longs to gain legitimacy and respect as the new Hokage and defend his people. Monkey D. Luffy wants to make history as the next Pirate King. Izuku Midoriya aims to use his new One For All Quirk to replace All Might as the next symbol of peace.
These goals can easily sustain a character arc, but "defend my friends from Hollows and catch up on homework" compares poorly. Ichigo simply isn't ambitious enough to win over the readers' hearts beyond the Bleach anime's first season.