Contributions are not credited

[AndreMiras]

Thanks for such a nice library.
Today I was checking closed/merged pull requests to try to understand what are the guidelines for getting a pull request merged and I realized none of them were merged.
While a lot of them were actually accepted and made it to the code base, none of the authors appear as contributors.
Is there a reason for that and could we do anything to improve the process so contributors get credited?
I'm a maintainer of a few open source projects myself and I get that sometimes you just want to get things a bit your way and you may not have time to iterate back and forth, but I believe crediting authors is important still and it's worth the effort to find a way to do it