The content of these cheat sheets describes what a music major learns in the first semester or two of music theory classes. But there are people who get PhD's in music theory. What do you think they study for all those years? It's not this.
Saying this is music theory is like saying arithmetic is math. It's not wrong, exactly, but it's leaving out a lot. People spend the first 12 years or more of their math education learning the notation, learning formulas, at least partly because you need to know that stuff in order to do any real math (we'll leave the discussion of whether this is the optimal pedagogy for another day, shall we?). You could say, "but people googling math want to understand why 2+2=4," but if you don't know that 2+2=4, there's not much point in trying to learn why. You could also say that what people learned in high school is what most people call math, but we all know that what people learn in high school math doesn't have much to do with what real mathematicians do.
"Real music theory" uses the contents of these cheat sheets (and many, many other things) to describe pieces of music and to try to understand things like: why did this composer choose the notes and rhythms they did? What can we use to justify the subjective observation that a composer or time period had a unified music style? What are the assumptions of musical language that govern musical composition without necessarily being known to the composers? Why does this collection of notes have meaning? What is that meaning? What does the content of this music tell us about how it should be performed?
The best of my music theory classes tried to keep a clear line from what we were learning to the kinds of questions above. The worst classes we spent a lot of time doing worksheets with the musical equivalent of times tables and algebraic equations, ad nauseam.
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I'd also like to note that the things that appear under the aegis of introductory music theory are a strange hybrid of techniques, reflecting the multiple purposes of music theory for theorists, musicologists, composers, and practitioners. So you get things that don't help much with analysis, like species counterpoint (probably a useful exercise for composers, and maybe for musicologists since it is really a historical curiosity, but not really useful for anyone else) or realising figured bass (really only necessary if you're going to be performing baroque music in period style on a keyboard instrument).
You could again say similar things about high school math of course.