I have a few reasons:

1. I subjectively just like it better. Things like dtrace, jails, the init system, just click for me.

2. I think it's good to not support a Linux mono-culture. Yes, there is Windows and macOS, but in terms of open source OS's, I think it's good to have more than one choice and so for any rough edges in FreeBSD, I'm willing to deal with them to support that goal.

3. I don't think you'll find any actual, hard, technical reason to want to prefer FreeBSD over Linux on a desktop. Anything you can do in FreeBSD you can do in Linux. Heck, FreeBSD is probably even running the Linux version (for example video drivers).

But really, which Linux do you mean? Nix? Gentoo? Red Hat?