I think the school rule that my kids lived with in the 90s and 2000s about not being allowed to use Wikipedia as a source was, in part, based on (now out-of-date) skepticism about its reliability compared to other sources. No one source is 100% (or maybe even 95%) reliable. Wikipedia is pretty good.
But, to the extent the rule still exists, I think it is also about trying to get students to dig down and use multiple, more direct, sources (eg, use the materials cited in a Wikipedia article). Heck, I remember back in my day, my teachers didn't want me to use Encyclopedia Britannica as a source -- they wanted me to go to the library and research a number of more direct sources. Kind of like the Wikitree preference for primary sources over secondary sources.