Why is Wikipedia a trusted and reliable place to start to learn about something?

From Wikipedia’s stated editing policy:

“Wikipedia’s content is determined by published information rather than editors’ beliefs, experiences, or previously unpublished ideas or information. Even if you are sure something is true, it must have been previously published in a reliable source before you can add it.[a] If reliable sources disagree with each other, then maintain a neutral point of view and present what the various sources say, giving each side its due weight.

Each fact or claim in an article must be verifiable. Additionally, four types of information must be accompanied by an inline citation to a reliable source that directly supports[b] the material:”

Is it perfect? No, of course not. But if you are legitimately and sincerely researching a topic, then you are never looking at a single source. As in, never ever.