I use Linux instead of FreeBSD because I'm old and lazy. I used quite a few alternative operating systems in the past. BeOS was my main OS for a while, for example. It was a great experience but there were also many drawbacks which required fiddling. And fiddling is not something I want to be required to to to make an OS usable.
I only run desktops and in the end it boils down to hardware support which is less of a problem under Linux, eg. Intel directly supports Linux while the GPU drivers have to be ported to FreeBSD at a later time.
I do not interact with the kernel myself, so I do not care about kernel APIs and such. I rarely use the command line these days, so the 1980's GNU userland vs. BSD userland debate does not matter to me.