When I bought mine, Amazon didn't have USB C and page turning buttons on the same model. Kobo did.

It has direct integration with borrowing books from the library.

It has direct integration with Instapaper.

You can drag a file onto the device after mounting it over USB.

You can replace the endpoint for the store with a Calibre Web endpoint to directly sync your books from a personal server.

You can pretty easily modify the device however you see fit.

For me the library integration on the device itself was a major selling point. I have no complaints after switching four years ago!

It's a much more open reader, you can literally drag a file into the SD card and install whatever software you want

I think a lot of it is due to people just not liking Amazon.

As a counterpoint, I bought a kobo (clara?) two years ago, and ended up hating it. It was a lot of minor things that added up. Spuriously turning on in my pocket/bag constantly and ruining progress (the power-on button was poorly placed and very sensitive). Forcing a single font for every book. Page turns were often noticeably slow. Libby/Overdrive integration often spuriously re-downloaded books and lost my progress. It was never clear to me whether I got unlucky with a bad device or not. But none of my issues screamed 'broken' rather than just 'annoying' so I assumed it was normal. I dislike the kindle ecosystem as much as the next person, but I've found the hardware so much better and more reliable that I ended up going back to kindle. The positive vibes in these comments are leading me to reevaluate and think that maybe something was indeed wrong with my device.

I switched to kobo for a while but I thought the hardware itself was inferior. Maybe they fixed it but I couldn’t dim the screen low enough to not annoy my wife while she tried to sleep. It felt cheaper too. I begrudgingly switched back to my old kindle.

You can sideload books on Kobo over USB they parse the expected formats epub/pdf/html without problems. There is custom firmware available and a homebrew app community.

I find their default interface is also good and can read anything without mayor problems, books, web & comics. My reader Elipsa 2e is also great for taking notes and supports notes in book pages, though that specific model isn't supported by the custom firmware.