I work in this space and can provide a little correction/illumination:
The folks selling printed phone cases, gameboy cases, etc are generally not shipping these over from aliexpress. They are almost all printed on demand from printers local to the country of the buyer (there's a half dozen big phone case printers just in the US). Nothing is mass produced except the blanks.
The sellers come up with the artwork and titles/tags/descriptions/etc. Software like mine creates the Etsy listings and processes orders, routing to appropriate printers which ship directly to the customer. Etsy provides an API for this.
Print-on-demand sellers are selling pure intellectual property. They jealously guard their high-resolution images, but that doesn't stop the industry from having a big ripoff problem. Low-effort ripoffs copy a public low-res image, which makes a terrible print but potential customers/victims might not be able to tell from an online mockup image. High-effort ripoffs involve hiring an artist to make a new work substantially (or identically) similar to something else. Both cheat the intellectual property of the original artist, but they're using the same print companies.
Whether this stuff is "handcrafted" is somewhat ambiguous - is a book handcrafted? Is a set of patterns for a dress or a piece of furniture handcrafted? Something 3d printed? Certainly someone came up with the artwork "by hand", but printing it on a tshirt or phone case is pretty mechanical.