I'd say there's significantly less gatekeeping on Wikipedia than most parts in academia. YMMV.
But: there are a bunch of random clueless people trying to promote their obscure papers to boost their citation counts, push weird nationalist POVs, add fringe pseudoscience, make "fixes" that turn out to be wrong, add vague explanations which they find personally helpful but nobody else can make sense of, remove clarifications and explanations in the name of rigorous purity, change the wording of sentences that have been subject of years-long dispute and careful compromise, and so on. Wikipedia maintainers are constantly fighting against these agents of entropy (or when an article is not actively maintained, it tends to get a lot worse over time), which unfortunately can sometimes also negatively color interactions with helpful contributors. They're also part-time volunteers, and fallible humans; try to cut them some slack.
To the extent that there is "gatekeeping", it is mostly along the lines of: you can't use Wikipedia primarily for self promotion, you can't add your own new claims that have no published source, and you have to abide by existing norms of project/community engagement. In general, people are judged by their contributions and behavior, not their credentials (though editors also include a bunch of world-class experts in the topics they contribute about, and it does have some pull when someone can say "I literally wrote the top cited paper about this" or whatever).
But beyond that, the difficulty is that there's no one correct way to explain difficult topics, no single audience for Wikipedia articles, a lot of strong opinions about how things should be one way or the other. Trying to satisfy everyone takes discussion and compromise and sometimes a minority is still unhappy with the resolution. The biggest problem though is that there are not enough active participants (including in mathematics) to write great articles about every topic, and writing a really excellent article about something takes a huge amount of work; there are many mediocre articles that have never really had the time put in to make them great.
When someone new to the project gets into a heated dispute about a minor point, they routinely get extremely frustrated and occasionally then run around the web complaining about how awful the people on Wikipedia are. Several times times in the past few years I have asked such complainers for specifics, and remarkably I have gotten a reply ~4 times. In all but one case, when I went to investigate further it turned out that they were clearly in the wrong. In the last example there was a misunderstanding and I fixed the issue. If you want to provide a specific article and error, I'm happy to go take a look.
Alternately, when people run into an unresolvable dispute on one local article talk page, they can seek opinions from wider groups of Wikipedia editors, e.g. on the math "wikiproject" talk page https://en.wikipedia.org/wiki/Wikipedia_talk:WikiProject_Mat.... If you make a post there about your issue, you will get more eyes on your problem, and it will likely be resolved correctly.
I'd say there's significantly less gatekeeping on Wikipedia than most parts in academia. YMMV.
But: there are a bunch of random clueless people trying to promote their obscure papers to boost their citation counts, push weird nationalist POVs, add fringe pseudoscience, make "fixes" that turn out to be wrong, add vague explanations which they find personally helpful but nobody else can make sense of, remove clarifications and explanations in the name of rigorous purity, change the wording of sentences that have been subject of years-long dispute and careful compromise, and so on. Wikipedia maintainers are constantly fighting against these agents of entropy (or when an article is not actively maintained, it tends to get a lot worse over time), which unfortunately can sometimes also negatively color interactions with helpful contributors. They're also part-time volunteers, and fallible humans; try to cut them some slack.
To the extent that there is "gatekeeping", it is mostly along the lines of: you can't use Wikipedia primarily for self promotion, you can't add your own new claims that have no published source, and you have to abide by existing norms of project/community engagement. In general, people are judged by their contributions and behavior, not their credentials (though editors also include a bunch of world-class experts in the topics they contribute about, and it does have some pull when someone can say "I literally wrote the top cited paper about this" or whatever).
But beyond that, the difficulty is that there's no one correct way to explain difficult topics, no single audience for Wikipedia articles, a lot of strong opinions about how things should be one way or the other. Trying to satisfy everyone takes discussion and compromise and sometimes a minority is still unhappy with the resolution. The biggest problem though is that there are not enough active participants (including in mathematics) to write great articles about every topic, and writing a really excellent article about something takes a huge amount of work; there are many mediocre articles that have never really had the time put in to make them great.
When someone new to the project gets into a heated dispute about a minor point, they routinely get extremely frustrated and occasionally then run around the web complaining about how awful the people on Wikipedia are. Several times times in the past few years I have asked such complainers for specifics, and remarkably I have gotten a reply ~4 times. In all but one case, when I went to investigate further it turned out that they were clearly in the wrong. In the last example there was a misunderstanding and I fixed the issue. If you want to provide a specific article and error, I'm happy to go take a look.
Alternately, when people run into an unresolvable dispute on one local article talk page, they can seek opinions from wider groups of Wikipedia editors, e.g. on the math "wikiproject" talk page https://en.wikipedia.org/wiki/Wikipedia_talk:WikiProject_Mat.... If you make a post there about your issue, you will get more eyes on your problem, and it will likely be resolved correctly.