A lot of companies are specialized in hacking the standards for testing. Depending on the company they use some of these tricks: These are all small sample sizes (around 100) picked from huge numbers of tested people (10s of thousands). They look at short term results, long term effects failed dramatically in animal testing. They use tests that can give false positives (PCR>26 cycles), and/or false negatives. Or just look at symptoms that are similar to flu. They do not have a proper (long term) placebo group (why not also use untreated patients as well). Other factors with huge impact as health, habits, food, Vitamin-D.
Big pharma wants to collect "their" billions for their medicine. Which is why we cant have nice things. (Or cheap medicine that do work well).