Curate, connect, and discover
I've thought about this way too much so I think I'll just dump every single intelligent thought I've had in my life here. There's three main ideas that I have regarding this and you could really just pick and choose the ones you agree with most, choose one that makes the most sense, or say that they all happen at the same time. I'm just a rando on the internet. You don't have to pick up what I'm putting down.
Okay, first things first, the most obvious answer is that there's probably just been a whole lot of chaos going on since the Calamity first emerged 100 years before the events of BOTW and far beyond TOTK. The entire kingdom was decimated by the Calamity and most of Hyrule wasn't able to properly rebuild until the end of BOTW when Calamity Ganon's influence was sealed/destroyed. During this time, I'm pretty sure most people either thought Zelda was dead (don't trust me on this, I don't really remember for sure) or knew that she'd sealed herself inside Hyrule Castle but at that point, there isn't much they can do to recover her. Formalizing her title as a queen probably wasn't their priority or even much of a possibility until she returned. And that brings me to my second point.
So not only was it kind of impossible or at least not worth it to change Zelda's title during the Calamity but I also think there would have been bigger priorities after she returned. This is probably the closest to your theory, in which there's just been so much going on between BOTW and TOTK that no one's really been that concerned with Zelda becoming the official queen. In this new post-Calamity Hyrule, it's very likely that people just accept Zelda as some sort of a leader figure regardless of her title not only because she's the last of the living royal bloodline but she also basically saved them all by sealing Ganon. Between that level of respect and the fact that there's so much rebuilding and healing to do across Hyrule, I think it makes sense that everyone's got enough on their plates right now without dealing with authority figure dilemmas.
The last point is probably the most important one to me and it's that Zelda probably doesn't want to be so tied up in royalty and titles anymore. We can see in the flashbacks in BOTW that she clearly grew up her entire life not being given a choice in accepting her predestined fate. This fate essentially had two facets: being the next Princess Zelda in a long, long, long, line of descendants of the goddess, and being able to seal the Calamity Ganon. It isn't too much of a stretch to assume that she sees those two things as very tightly connected traumas. And after sealing Ganon, she's free. She is heavily implied in TOTK to be living as normal of a life as possible in Hateno. For the first time in her life, she has the freedom to be whoever she wants to be and do whatever she wants to do.
So yeah, I'd like to think that Zelda chooses to keep her old title not out of fear of responsibility but simply out of respect for the past and also chooses not to be Hyrule's queen because she knows that Hyrule is different now. She's changed and grown as a character and her role in leading Hyrule has also grown as the people she leads have changed over the 100 years she was stuck in Hyrule Castle. She will forever be 'Princess Zelda' to some people and 'just Zelda' to others and I think it's beautiful that she gets that second choice to live her life the way she wants to live it.
can anyone who knows the lore better tell me why (at least in the botw/totk era) princess zelda is still princess when technically she should be queen since king rhoam's death or does the ascension of royalty in this universe's monarchy different i'm genuinely curious
(i mean, i suppose, the events of botw and then totk might have been the reason why she isn't queen yet)
(also, on a completely different note, tell me why i saw someone on twt say that, and i quote, "link canon wise is christian")