I don't think that series is available DRM-free anywhere, since it's published by Random House.
The publishers and/or distributors decide if DRM is applied to books on Kobo.
It's a shame, I love Neal Stephenson's work, and would really like to read that particular series again as an e-book.
@mykhas
I'm not sure about that particular title, but #Libreture has a list of DRM-free book shops here:
https://www.libreture.com/bookshops/
The admin is @kevinbeynon