Someone asked me that and I immediately thought, that's a great question! There are several reasons I approach things the way I do.
One of my big goals is to help people come up with replacements for the (usually unintentionally) ableist social skills curricula that are currently getting used. They seek to teach neurotypical norms, so a replacement needs to be about neurotypical culture.
If someone comes to see a speech therapist, they're generally looking for sessions where I'm working directly with the neurodivergent person, not the neurotypical one, so my resources match that accordingly. (Although I agree that neurotypical people could stand to learn about neurodivergent people every bit as much as neurodivergent people could learn about neurotypical people!)
To be honest, you also can't teach "neurodivergent culture" as some monolith. The idea of there being one neurotypical culture is already a stretch, even if you're confining it to the majority cultural practices of a specific region. Once you move to neurodivergence, there are just way too many different ways in which it's possible to be neurodivergent to pin it down to a culture. And depending on the specific neurodivergence, their needs and practices can actually completely conflict with each other. There are definitely themes among neurodivergent people overall, but if you really wanted to learn about a specific culture, you would need to learn about that specific neurodivergence.
How Can I Learn More About Neurodivergence Generally?
If you want to take a deep dive into the subject generally, honestly, I'd recommend the Wikipedia page on neurodiversity. They do a really sweeping job of covering a whole lot in just one article and it's hard to beat.
How Can I Learn More About a Specific Neurodivergent Culture?
A good place to learn is any place run by people with that neurodivergence themselves. Read, watch, listen, and learn! Because autism is the neurodivergence I have the most experience explicitly and intentionally learning about, I'm going to use the lens of how I learned about Autistic culture to give you ideas that you can apply to learning about other neurodivergent cultures.
First off, books by authors who have a specific neurodivergence themselves are definitely important to learn from. Books most directly related to Autistic culture that I have loved are "Loud Hands: Autistic People, Speaking" and "And Straight on Till Morning: Essays on Autism Acceptance". I have also heard excellent things about "Neurotribes: The Legacy of Autism and the Future of Neurodiversity" although I haven't read it myself.
Reading lots of blogs or following social media pages from people with the specific neurodivergence you're learning about is always a good move. I've always loved Judy Endow's writings. My favorite of her posts is "Assigned Friends". Julia Bascom also has some incredible writings. My very favorite of her blog posts is "Quiet Hands".
I also think it's useful to read a bit about gatherings run by and for people with the neurodivergence you're learning about, because that's a space they have in which to be the most themselves. AutCon is a conference by autistic adults for autistic adults. The list in their FAQs of what they have in place at the conference to keep the environment "autism friendly" is actually a really good reflection of Autistic cultural norms and values.
You might find answers from vloggers on YouTube, like I found with the great "Ask an Autistic" playlist covering common questions. Social media forums often have areas where you can go to ask questions about neurodivergence. For instance, Reddit has a whole "Ask Autistics" subreddit where you can ask questions of actually autistic people, and I know there's a similar page on Facebook.