There could be a variety of factors for why they weren't confirmable that aren't immediately obvious even if you followed the methodology.

Not only psychology the same thing involves a lot of different disciplines. It may not be possible to confirm some results without additional study requiring much more money and resources anyone is willing to put in to it.(and the returns may not be worth it)

As an example, my M.S. final capstone work in Occupational Safety management involved a analysis of multiple different statistics involving commercial aircraft operational safety outcomes and multiple other factors likely linked to them.

Took 20 years of recorded statistics, looked at likely correlations and known historical changes with regard to various technologies used in the field.

The only thing my 40 odd pages of analysis points to are likely or very high levels of positive & negative correlation and likely related variables leading to them...

There is no way in hell to say for any absolute certainty that what factors really affected the long term outcomes as they number of variables are too numerous. The results were significant, they contributed in context to the discipline and all that jive... now, if one would want to try and confirm the outcomes to be 100% sure outside of the statistics it would probably take few tens of millions of $ and a decade or two of work with a lot of staff around the globe. Still even then the outcomes would likely not be repeatable for sake of the original study performed. One could do a study on likely levels of positive and negative correlation between variables between them -.- ....