The majority of Article sites are not auto approve, so unless your article is very well written, it wont get through. Media Wiki is not really an article site at all, you are just posting content onto a profile page, which is Auto Approve, so you see more success.
Just because GSA can post to hundreds of different platforms in one go, doesnt mean that is the best way to go about it.
If you are particularly interested in posting articles, go check out some AMR threads for best practices (such as content length etc) then apply them to GSA and test.
Same applies for other platforms. If there is a popular, dedicated software for the platforms you want to post to, read up on that softwares best practices and apply them to GSA.
GSA is incredibly powerful, but with such a diverse list of target platforms, it will take a while to dial them all in perfectly. Test each platform, and if you spot a bug (eg fails on a specific platform version), either report it to the developer with full details (PLEASE dont waste his time with vague questions) or if you dont know how to test in detail, report it on this thread and me or others can test more thoroughly.
That said, it does work great 'out of the box', but you can squeeze more out of it by following these steps.