As mentioned in the other recent thread about Wikikpedia, I am a Wikipedian. I joined active editing in 2010, that is after the heyday of welcoming new editors, but long before most articles on important topics were anywhere near to being well sourced. I have tried to clean up the mess on some articles, and am a winner or co-winner of two Million Awards[1] for fixing up high-page-view articles.
But how I got the awards basically illustrates the problem. One article I fixed I wrote entirely off-line in a text editor file, while commenting on the talk page of the previous lousy version of the article, and then I dropped in the new article text all at once. Every previous time when I tried piecemeal editing of that article, my best edits would be reverted, while other stuff that was entirely made up and without reliable sources would be inserted into the article. The second article I worked on fixing up was a collaborative effort. Again, I started with discussion on the article talk page. My first few edits were reverted, contrary to reliable sources, by editors who exerted "ownership" on the article but who refused to look up sources. Later I was joined by two other editors, and one of the other two made it his project to rewrite the article from top to bottom for one of the Wikipedia editing contests. He liberally threw out old unsourced crap and then layered in new, well sourced text. I mentioned on the article talk page I'd like to fix a few sections of the article, and proofread all of it, and after he deleted the old crap, I put in new good content in the sections I worked on and checked all of his references throughout the article. The former editors who let the article be bad for years slithered away. It's a slog and a struggle like this every time someone tries to improve Wikipedia--the established editing culture includes snap judgments without looking up reliable sources.
AFTER EDIT: I also mentioned in the previous thread about Wikipedia that I hope sometime soon a philanthropist funds a Free Online Encyclopedia X Prize to put to the test what could be possible in building an accurate, well edited free, online encyclopedia if some new projects began and tried out some new models of project management and perhaps some new software. (I personally don't have any trouble dealing with Wikipedia's software, but I have been using various kinds of markup languages since the 1980s in earlier editing work.) The only way to know what's possible is to try to challenge the incumbent project with some competition, I think. Even if Wikipedia then just ended up winning a prize with reasonable criteria, it would still become better, and we would all have a better idea about what works and what doesn't.
[1] https://en.wikipedia.org/wiki/Wikipedia:Million_Award