1. BSD was, at the time the Linux kernel was written, still in legal disputes on the matter of the copyright of its code.
FreeBSD came into being in 1993, about 2 years after Linux first hit the servers. Linux was massively incomplete (compared to today) at that stage, and both have grown up more or less in parallel. FreeBSD itself has earlier origins, 386BSD, etc, which go all the way back to 1976; Linux was just 6 years old at the time and, gifted though he is, I doubt he was writing Linux back then.
2. Linux was written from scratch, mostly ... the kernel, I mean. The userland tools as well ... now, you will certainly find this or that, such as the zfs implementation ...
What, there's no BSD-inspired code in there at all? Not one single line? I don't really care, but I bet you cannot prove that.
Now, how is this any worse than what GPL types do ? I mean, GPL'd code is freely available, provided you stick to the license - it is not. GPL is there so that proprietary competitors do not use the work of a gazillion devs in their proprietary BS.
Are you crazy? GPL is cool with usage in proprietary systems so long as the terms of the license are adhered to. There's no "For non-commercial uses only" clause like there is in some proprietary licenses (eg VMWARE Player, a great proprietary gift to the world). Linus even resisted transfer of Linux from GPL2 to GPL3 to ensure that use of Linux didn't drop off as a result.