Maybe communities like to think of themselves that way, and if it were really just based on "skill" that would be less of an issue. But in reality these things are more often based on who you know. In most open source projects, no matter how good my patch (or bug report) is, if I'm not friends with a maintainer it will be ignored or rejected. Same for Wikipedia. The quality and skill of the actual contribution is practically irrelevant, it's mainly about the pissing matches with other "editors": if you have time to babysit the page and undo reverts, and then navigate their hierarchy and appease the right people before you get banned. Most people won't bother: they will add some information they know, see it get reverted, and never try again.
What page did you edit, land in a pissing match with an editor, babysit reverts on, and then end up getting banned for working on?
In fact, to make it simpler: what page did you edit on Wikipedia in which any of these things happened? The nice thing about Wikipedia strife is that it's all archived, so let's talk about specifics.