[Quoth]

Many places are gone. Amazon has 90%.
Most publishers don't sell direct (we removed it too)
Even Google struggles to sell much variety via Google Books/Playstore. So we upload to Amazon and Smashwords. Smashwords means our books are on Kobo, Tolino, Apple, Nook too. Smashwords also sell to libraries / Overdrive I think, we've had sales to all that Smashwords distribute to except libraries. We never sold any on Google, nor direct. About 2/3rds are via Amazon.

So I'd expect majority of more recent readers to buy 1 source only, Amazon mostly (90%) or the ePub ereader associated shop, and then next group 2 to 3 shops (maybe some Kindle owners from Smashwords and people with Nook, Tolino or Kobo sometimes from associated shop and maybe Smashwords).

I bought an ereader about seven years ago purely to read PD Gutenberg. The niche publishing for half a dozen people was later. I've bought very few ebooks compared to paper since. Only were there was a big discount or it wasn't on paper. Only from Smashwords and Amazon.

It's very sad. Partly the idiocy of the big publishers not having 100% of their titles on eBook and POD on their own portal and better ebook pricing. Supermarket mass market paper is cheaper than ebooks from same publishers!