Of course Wikipedia is not a reliable source. This is something well-known across Wikipedia as well: we do not cite Wikipedia in Wikipedia articles, nor would we cite any wiki with user-generated content, because they are inherently unstable, unverified, and unreliable.
Now here is a major reason why Wikipedia is left-leaning. Wikipedia is based on reliable secondary sources, and so vetting those secondary sources is something that takes up significant effort among editors. The problem is that many right-leaning sources (Breitbart, The Daily Caller, LifeSiteNews et. al.) are considered by Wikipedia (and many other reputable orgs) to be completely unreliable and have been blacklisted from the list of sources usable on Wikipedia. There are comparatively few left and ultra-left sources that have been found fabricating stories and publishing lies, and therefore, Wikipedia is content to use a preponderance of left-leaning sources due to their better reputation. The editors may read such sources on a regular basis, and so I regularly see NCReporter and RNS preferred to NCRegister and CNA in Catholic topics. It is possible to put together good articles that are neutral by picking and choosing good scholarly and book-based sources that are not left-leaning. But the leftism always trickles in eventually. It also hurts us that many right-leaning and conservative editors have been blocked and exiled from the wiki due to not knowing/caring about the policies and guidelines in place regarding editor behavior and article content.
There is a section in Wikipedia called WP:RGW, and it basically tells us that we cannot expect to come on Wikipedia and “right great wrongs” in the world by our editing behavior. Wikipedia tends to reflect the world and moreover reflect its editors, so until and unless more good-faith editors with a less than left-wing bias come on and contribute meaningfully to the project, the left-leaners will always dominate, and that is nobody’s fault but ours.