FreeBSD networking during WhatsApp and Netflix starting era was definitely better than Linux. Both in their specific usage pattern. So it wasn’t some ideological reason but actual technical one. But that was 10+ years ago.
If I remember correctly from reading Meta / Facebook successfully switch all of WhatsApp large bare metal 4U server to their standardise Linux blade by 2017. They also spent 3 years working on Erlang BEAM and Networking so it was working close enough.
Netflix continues to use FreeBSD and it is working well for them. Both the lead engineer comment and submit update on HN frequently. Do a search and it should be easy to find it. ( on my phone now so can’t quote links )
2022 now I think any general advantage of FreeBSD over Linux in networking performance would likely be minimal. But it also doesn’t make sense to switch to another for the sake of OS unification.