Is it just to check that the paper's results are correct? Should I expect that the authors describe their methods for arriving at the right answers / solving a problem? I've often found that on a key part of the paper, e.g., the main result, the authors just give you the data without explaining. I then have to verify that the data is correct and the results are correct but this takes a bit of work on my part, which I am happy to do, but I wonder why these steps aren't shown on the paper itself.
Is what I described the usual expectation when reading a research paper? That I shouldn't expect researchers to divulge how they arrived at the right answer and perhaps that is a way for them to protect their work, e.g., whatever method they came up with that worked ... could have the potential to be used again and again to publish more papers?
I also tried contacting researchers directly to discuss their work. All of them are happy to talk - but mostly on a superficial level, e.g., "I've done X,Y, and Z, my co-author has done A,B and C."