It would be great to be able to use Evernote in Linux (being a Linux user for the past 12 years, I would love it, but I am not holding my breath).
Unfortunately the trend is not in favor for making Linux clients for a number of reasons
smaller market share (compared to Windows) requirement to port or adjust coding for the *nix environment (OS X is BSD-based which is similar, but different), this includes different desktop environments (KDE, Unity, Gnome/Xfce/Lxde, etc.) packaging for the different distributions (.rpm, .deb, etc.) and different distributions file layout
To make it worthwhile they need to either
Release the client as open source, so the different distributions can have their own package managers take the source code and compile it for the distribution Make it in a cross-platform manner so they only have to write it once
These days, #2 is where companies are going! I haven't been able to try the Windows client before, but outside of Java the best cross-platform desktop (laptop) client available is a web interface.
This is currently the best write-once-run-anywhere solution.
And Ubuntu (at least, others are too) is pulling in web applications into the environment as first-class citizens and making the line between native/local apps and web apps harder to see.
Although I really wonder how much tweaking there really needs to be to convert an Android version to run
Here's another well known app that is not available for Linux (despite the company promising they would make one... 5 years ago!) and so you are forced to use 3rd party FOSS apps instead: Google Drive
You may not use it, but a lot of people do and it is almost the same exact situation as Evernote.