There seems to be a few issues at play. First is the "file drawer effect". If the experiment doesn't show a positive (or surprisingly negative) outcome, then it's most likely to get filed into a drawer and forgotten.
The second issue is just random luck. Suppose you flip a coin 10 times, then it's possible that you might get a run of nine heads and one tail. Based on that experiment you could publish a paper that the coin has a 90% chance of flipping heads. That would be a surprising result, and it's likely that it would be debunked if anyone tried to reproduce it.
The third issue is that it's exceedingly rare for anyone to try reproducing an experiment. There's no grant money for reproducing experiments and regardless of the outcome it's unlikely to advance a researcher's career.
Together these mean that most published papers could very well be the product of random luck that will never be verified.