Question about Structure

I think you're taking the concept of developing idea a bit too strictly/literal. All the sections you pointed out can be thought of B or C themes or transitions; those ideas also have the quality of creating self-sustaining patterns, by repeating the musical phrases 2 or 3 times. Moreover, the main theme can only be interesting if you pull away from it and come back to it in a dramatic way. If you don't wander away from an idea briefly, you're not moving the musical narrative anywhere.

To use an analogy: you could be telling/writing a story that is all about one main character, and most of it will be spent describing their feelings/actions/dialogue. However, even if the story will be MAINLY about this one character, you still need to spend a few words talking about what environment they're in, or give some background context, talk about the setting [...]. So not every single sentence will have the character's name in it. People can bear quick detours from the main subject, and these detours can actually enrich the story (or the music) in many infinite ways.

A good things to practice is to see how far away from the subject you can go without losing people's interest, because the more you can do that, the more satisfying the return will be.

However, no amount of intellectualization will teach you how to structure your pieces; transcribing/studying music, composing, and (more in general) experience will give you the tools to understand the structure of this piece and other pieces. Trust your intuition as a listener for other composers' music, and trust people's feedback about your compositions. Don't worry about the "there were only 4 bars of theme B, while I thought you only needed to have 2, but sometimes it's 8...?". I could explain and analyze something for hours to you, but that wouldn't give you a deep understanding of what the music.

Did you like the composition? Did it make sense to you? How did you feel about the flow of the piece? Do other people respond positively to it?
That's all it matters anyway, there are no hard rules. Mike talks about "principles" but rather than taking them as gospel you treat them as directions and figure out what works for you. Arrive at your own conclusions and you tell me why this piece works (or doesn't) in your opinion. The process of doing this will teach you more than reading me breaking it down.

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P.S. when you're done transcribing it, I've done a transcription of this piece myself a while ago which maybe is useful: https://redbanned.com/threads/transcription-requests.77/page-2#post-7603
... but don't peek before you're done transcribing it yourself