For the same reason you don't trust the politician when they say something self-serving, you don't trust a bike company with their wind tunnel data. I don't entirely think they fudge the data, but they almost certainly pick wind tunnel settings and tests that will be most favourable to their frame and unfavourable to the competition's.
Similarly, you can't really trust most magazines' tests since they're usually accepting cash for ads, and the sometimes-unsaid proposition there is "we buy five digits worth of ads, you say nice things about our bike".
Actually-independent owners that aren't trying to sell ads or pageviews can be trustworthy since they don't have conflicts of interest (other than not wanting to tank the resale value of their frame), but it's going to be rare that you can get enough bike owners together at a windtunnel and put on a good test. And even if you do put on a good test, you may just inadvertently pick test parameters that favour one frame over another, so you may get a false ranking anyway.
Basically, I'm utterly nihilistic when it comes to comparing frames. Way too many parameters to fiddle with and far too many huge conflicts of interest behind any data release.
This isn't unique to cycling: compliant car reviewers get access to nice vehicles, positive game reviewers get pre-release access and betas, journalists that uncritically parrot "anonymous government sources" are granted more access to future scoops. Disseminating accurate, unbiased information is a hard problem to solve in any industry when there's so many people with lots of interest in muddying the waters.
My favourite source of data is the kona top 10. You can't say "top 10 at kona = fastest equipment" since most equipment in the kona top 10 will be chosen by the sponsors, not the athlete. But you can say "this stuff is good enough that it didn't sabotage their race". Anything ridden to a top-10 finish may or may not be the fastest, but it's definitely good enough.
STAC Zero Trainer - Zero noise, zero tire contact, zero moving parts. Suffer in Silence starting fall 2016