Writing is honestly a lot of work. Like, sure, I can jot down things that are in my head and it comes pretty naturally to me. But writing anything decent requires research. A lot of research, so much research, a crazy amount of research. Yes, even if you're like me and you're a fantasy writer.
Like, sure, I can make up a world entirely, but to do so I need at least some understanding of geography, cultural differences, architecture, agriculture, etc. Writing means you have to have at least a base knowledge in a whole bunch of things.
And a lot of what I write happens to be modern fantasy: fantasy taken on Earth (or an alternative Earth), which means I have to look at real-world things.
My novel, Unicorn Valley, takes place in the United States. Which meant one thing that was important to me was including Native American lore, because the Native American tribes were here before anyone else. The beings they spoke about, the myths they drew and shared, were here too. But I can't just grab some lore and plop it down the way I can for European mythology.
See, with European mythology - that's encoded, in a lot of ways, into the US zeitgeist. In a similar way to the fact that the country is culturally Christian, it is also culturally European. You don't have to put in any work to learn about dragons and fairies. Sometimes, mythology and lore from other cultures creep in - djinn from Arabic cultures and Islam, golems of Jewish origin, the knowledge of Greek and Roman religion and myth - but it is overwhelmingly European.
Fantasy stories and novels require some modification of folklore. There are a lot of competing myths, and some things that won't fit the story. Every story needs to take parts of the myth and create something new that works for that story. However, despite this, it's also important to be respectful.
A perfect example of this comes to mind with the Native American mythos of the wendigo. For one thing, it's not "Native American". The wendigo is specific to . There is also power in names, and one could say I am calling the attention of the wendigo by using the name. However, I'm using the name in an informative manner.