
Because in its default enabled state it it causes a global performance hit on all system calls (https://fedorahosted.org/fesco/ticket/1311) and unwanted spam in dmesg, in particular when using Chromium (https://github.com/NixOS/nixpkgs/issues/13710).
*** NixOS *** NixOS is a Linux distribution based on the purely functional package management system Nix. More information can be found at http://nixos.org/nixos and in the manual in doc/manual.