Eh these days when it false flags pretty much all the rest of the major commercial ones do too because they're sharing data to be more robust. You're right that it's mostly just people using decade+ old biases against it.
It's not a bias, it still, to this day, pops up false positives more often than other firewalls.
And the people who believe false positives are also the same ones relying exclusively on Windows Defender and not using secondary firewalls, just a better firewall in general, or using real virus scanners to fact check the positives.
I still have Windows Defender on my system, and it fails to flag a lot of actual threats that my other firewalls do and tries to flag things that my other firewalls realize aren't malicious.