Netflix is doing 100Gbit HTTP and > 60Gbit HTTPS on a single socket Xeon E5 with FreeBSD. These servers are about 1/3 North American Internet by volume. In comparison to OCA team their AWS team sounds like a total tire fire to me in terms of engineer count and monthly spend.
I run the OS team at Limelight Networks, one of the largest CDNs. We can peak beyond 10Tbit/s on our current network and have to deal with a more demanding/unknown workload compared to NF OCA. This is all courtesy of FreeBSD. My entire management chain agrees that the cost of entry is lower to influencing and driving development in FreeBSD vs other kernels, and we collaborate with the other well known players on projects that are mutually beneficial such as TCP and filesystems.
Companies switching from FreeBSD to Linux usually are victim of the decision from bad VP-level management looking for a scapegoat rather than solving actual business and culture problems. Yahoo began transitioning to RHEL in 2005 and AFAIK are still at least two years from conceivably being off of FreeBSD. A 12 year _free_ OS transition is an embarrassing use of engineering effort and total management failure.
There are a lot of companies satisfied with FreeBSD, especially in the appliance space and small business, but they are not vocal because it just works and is often rebranded.