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Almost certainly because the most common opening sentence for an article follows the "[subject] is a member of [broader group]" structure and the more generalized you get, the more you get into entire areas of study, which are eventually classified as a kind of philosophy, which is just fancy-speak for "high-skill thinking."
There have been some theories on this phenomenon, with the most prevalent being the tendency for Wikipedia pages to move up a "classification chain". According to this theory, the Wikipedia Manual of Style guidelines on how to write the lead section of an article recommend that articles begin by defining the topic of the article. A consequence of this style is that the first sentence of an article is almost always a definitional statement, a direct answer to the question "what is [the subject]?"
Wrote a paper on this for a network theory class back in college and came to pretty much the same conclusion. Pages tend to lead to “funnels” of similar general topics, such as Earth, science, etc. and they all make their way upward into philosophy, which is the study of thinking, since thinking is at its core how we perceive the world.
Interestingly there’s two distances from philosophy that pages tend to hover around, the closer one of which is more full of technology and science stuff while the farther one is mostly places. It’s a pretty interesting deep dive