All of these terms describe an aesthetic that references the stereotyped essence of a way of life. But these new uses reference a way of life typically stereotyped to be approximately the opposite of "hardcore."
All of them put a little smile on my face, but prairiecore is my favorite: https://aesthetics.fandom.com/wiki/Prairiecore
Edit: Language is fun. There are eight replies to the parent comment so far, and almost as many interpretations of "core," with different connotations. We're all sitting here understanding the word "cottagecore" perfectly well, but having subtlety--yet importantly--different subjective experiences while doing so.
I must take exception though, as the American tallgrass prairie looks nothing like that photo. Checking wikipedia, that would be pretty indicative of perhaps the very thin shortgrass prairie from pretty far west (Colorado, Wyoming, New Mexico) where the cowboy lifestyle was prevalent?
Tallgrass prairie is gorgeous and very colorful.
Wiktionary [1] describes the "-core" suffix as a similar backformation from the musical genre name "hardcore", and as with "-gate", it seems to have developed into a general-purpose inflection denoting a genre or subculture - to the extent, I suppose, that those two concepts can any longer be distinguished from one another, at least.
": Cottagecore, a movement hearkening back to agricultural life, skills, and crafts, is on the rise. “As a concept, it embraces a simpler, sustainable existence that is more harmonious with nature. Aesthetically, it’s a nod to the traditional English countryside style, romantic and nostalgic,” says Davina Ogilvie, founder of Wovn Home, a start-up that makes custom (but affordable and accessible) window treatments."
"a central and often foundational part usually distinct from the enveloping part by a difference in nature" https://www.merriam-webster.com/dictionary/core
I.e. a <prefix>core person is one whose central foundational part is based on <prefix>. Material related to <prefix>core is from/for/focused on that type of identity.
There's an entire wiki of -cores: https://aesthetics.fandom.com/wiki/Cottagecore
Also like other comment about hardcore maybe being part of the etymology