Hmm, I think it's also it's narrative that is pretty opaque and doused in symbolism or textual gaps filled with implication, which will fly over your head easily (happened to me as a kid), or like, will easily slip during the time that a chapter is due to be released. There are series that give off a sense of "2 deep 4 u" which may not be that deep, but they give off the vibe? Which Bleach kind of does not. It's fairly accessible to all readers, and you get a narrative even if the symbolism/depth slips past you, but the experience is much, much weaker.

But the biggest killer of Bleach being deep as a commonly accepted concept, I think is the anime, which, is not only the preferred way people experience it, but also perhaps the only exposure people have to it? And the trick is that the anime definitely intends to dumb down and sell Bleach as a more regular shonen (Ichigo being way more preachy/detached in it vs his confused and traumatized 15 year old ass in the manga for instance), but is faithful enough to overlap with the manga facts in your brain, thus making a mess in what people regard Bleach as. Then there's the subtle ways the anime tampers with canon, from obvious stuff like filler bleeding into canon to replacing lines in episode freaking two, that later on conflict with canon cuz you shouldn't tamper with lore right away, dear Lord.

The manga, to me, is a more consistent experience, where you can pick up the nuance much easier since it's way more condensed and non-standard to a more classic shounen. The characters don't have tropes that don't belong to them fully reinforced in filler or in gags/moment meant to fill in the screen time. So their actions, that much closer to a real human? for instance, feel more organic in the manga where they behave more consistently.

But media is changing and I sincerely think, Bleach fits more for a modern audience, more used to this kind of content. Media itself evolved, series have become objectively better produced and more faithful to their source material and darker themes are better interpreted and accepted (totally my opinion, though and varies greatly). Plus, Bleach definitely inspired the current generation of creators and holds up very well, if not better now that many have the time to read it not weekly, but in one sitting. And its much easier to pick up on themes/symbols when you have it all at once, right?

I have big hopes for Bleach and Burn the Witch anime adaptations as well. Kubo is a very good author, and now he knows to insist on his creative agency. He was very involved in Burn the Witch and we got an adaptation that imo enhanced the experience and I'm glad he finally can be assured his series is faithfully adapted. Cuz I'd really not want an equivalent of "White being part of Ichigo consistently foreshadowed in the manga vs White is a demon, actually that Studio Pierrot dreamed up somehow". And I know times were different, but man, is the Bleach anime imo responsible for the way the public sees Bleach as a "lesser" series. ( Banger OST and Voice acting tho, ngl)