You have to understand that music theory is not a set of rules to follow, its a set of ideas that sound good to western ears and therefore are very commonly found in most music.
Not every song, but much western music, especially pop music and nursary rhymes, will stick to the same major or minor scale of notes for the whole song. Going outside of this scale is quite normal too and changing the scale/key multiple times in a song is also quite common.
The point of learning music theory is to give you a toolbox so that you can both recognise patterns in music you are listening to, as well as give you some ideas of what sounds good when you compose or improvise.
This is quite similar to mathematics where in school we dogmatically teach students how to do arithmetic in the base-10 euclidean system, because having deep fluency in one system is more useful than having a little understanding of many systems.
I certainly understand that in any system (not just music), some rules can be broken at certain times for various reasons (safety, aesthetics, etc.). To combine what you're saying with what I was saying, I would like to see, at least in this case, a better explanation of what exceptions are commonly made to these rules (e.g. using non-standard chords) and when they are made (e.g. in music from region XYZ).
In fact, I'd argue that such explanations are critical even when you're learning any kind of theory since it tells you when the theory breaks down, whether that's because it simply doesn't fit the task, because people like to get creative, etc.
You've missed my first point. It's not rules. There are no rules to break. The "broken rules" simply describes systems within music that you haven't been introduced to yet. For example, major and minor are also called "ionean" and "aeolean" "modes" respectively, and these sit within a set of 8 modes. There are also blues and jazz scales, names for music that break out of standard tuning. There is a style called "12 tone" (of which an example is Also Sprach Zarathustra) which uses deliberate dissonance.
You simply aren't up to that part yet, because classical western music training teaches the more common ideas which are in music that the punters listen to first. (Mainly because people generally need a few years playing music before they develope a taste for these things anyway)
Not every song, but much western music, especially pop music and nursary rhymes, will stick to the same major or minor scale of notes for the whole song. Going outside of this scale is quite normal too and changing the scale/key multiple times in a song is also quite common.
The point of learning music theory is to give you a toolbox so that you can both recognise patterns in music you are listening to, as well as give you some ideas of what sounds good when you compose or improvise.
This is quite similar to mathematics where in school we dogmatically teach students how to do arithmetic in the base-10 euclidean system, because having deep fluency in one system is more useful than having a little understanding of many systems.