We should have had them years ago.
There are two factors at play, I think: one is the lack of standardized access to digital technologies. As a narrow and personal example, during the pandemic, I have been severely limited in what technologies I can use in online or hybrid lessons because I have to make sure that all students can access everything equally and fairly. (This has been problematic for a lot of reasons, but the most surprising one was bandwidth.) So, in your example of replacing a diagram of a frog dissection with an online, interactive model I would need to make sure that all students could access the model; if it were an AR model, I would need to make sure all students had devices that could properly display AR tags and labels.
The second factor is that it is far easier to design a digital app, website, or ebook from the ground-up than it is to re-configure existing textbooks as hybrid versions. As an example, a lot of the textbooks I use have replaced CDs with online audio. It works well enough. However, if I were to build that textbook from the ground up as an app, I could have all the audio and video files embedded and playable from within the text itself.
But the truth is, I think even the best hybrid textbooks are just a stopgap. I predict that within the next few years, we'll see the promised full-color e-ink screens come to market and that will contribute to a rapid, full-scale shift in how textbooks are both produced and marketed. So, while hybrid textbooks would be nice, I suspect most publishers are trying to find new models rather than modify old ones.
Gatekeepers are tied to traditional and profitable modes of book sales and learning but I’d also say their a common denominator. They can reach most and don’t press the current system to change to elevate that common denominator.
Hybrid programs can help reach more learners in the current system, however. Rather than saying someone is just “not good” at a subject, the varied illustrations could illuminate it. The flexibility might actually attract more sales outside education because people would be able to learn something of interest in a new way.
Online courses have replaced a lot of the need for textbooks - hybrid or otherwise. The academic world is just slow to try newer methods that are obvious to others. As noted in the previous comment, it's a lot easier to build something new from the ground up than reconfigure existing textbooks.
I've been teaching guitar online for 20 years and it has become a very crowded niche recently. If you go into a music store today it's unlikely they even sell traditional guitar method books anymore. Music schools have gotten really good at engaging students online without books at all. As well as learning to play other instruments online, I've also studied foreign languages and taken courses on becoming a caregiver for my parents. There are courses for everything, and good course design for me is when I don't have to print a single page.
Some online schools do require students to buy books published by the school. For something with immediate and practical uses (eg. learning a foreign language, becoming a caregiver) I'd be skeptical of having to buy a book as well. University is great for many things, but when formal accreditation isn't the goal, there's probably already an online course for it that doesn't use textbooks at all.
I like the idea of more closely integrating print books with online resources. The publishers of MS and HS language arts textbooks provide tons of online supplements these days, but they're not an integral part of a lesson. One challenge is the awkward transition from one medium to another (no way to click a link in a book). Joel's prediction below about the shift to e-ink screens is intriguing.
Retired teacher here (3 years) ... HS Literature .... I virtually abandoned the textbooks 10 years ago. Only occasionally would I require a textbook-based reading. First, we became more reliant on novels, then later on secondary texts (online and otherwise) to augment the topics/themes being taught. Ex: When teaching Mary Shelley's 1816 novel "Frankenstein," supplemental reading might include related, non-fiction articles on latest scientific developments, such as the gene editing tool CRISPR, or human chimeras. Questions might be: how scientific ethics have really evolved over 200-plus years? Some of this kind of thing is already online; teachers have their own interactive sites which include capabilities. The point is, an app (as you suggest) is kinda, sorta already being done ... just a little more clunky in its functionality.
Now, addressing the problem of student attention is quite another issue. When that notification "ding" from Instagram sounds and the dopamine kicks in, how to prevent the students' lizard brains from quickly abandoning the app to see who "likes" them.