Three basic reasons:

1. Learning a brass instrument is complicated and challenging compared to traditional classroom instruments:
   • Basic sound production on a brass instrument requires significant embouchure and respiratory system development (especially in comparison to the recorder).
   • Unlike woodwinds, strings, and Orff instruments, where you can see the position of each note and how they relate to each other, brass instruments operate on the harmonic series (hidden from view) which requires development of aural skills and more precise pitch production.
   • Adding valves, slides, and reading music notation to the above points creates layers of variables that can make teaching beginning brass in a whole-class setting extremely challenging.
2. Most teachers assume that they cannot teach brass unless they have a brass background - that teaching brass requires specialized knowledge and training. It creates a self-perpetuating cycle: Since few teachers are exposed to brass in their formative years, few would feel capable of teaching it.
3. Cost & upkeep: Brass instruments are expensive to purchase, costly to repair, and the regular maintenance to keep valves and slides in good working order can be significant, often eating up valuable instructional time.

In short, equity and access:

The 2015 U.S. Federal K-12 Legislation, Every Student Succeeds Act (ESSA), stipulates that music and the arts are a necessary part of a well-rounded education. Although specific requirements are left to the states, and there are enduring problems with overall access and equity across the U.S., over 90% of elementary school students have access to a general music education, but less than 4% of students end up learning a brass instrument.

According to the National Association for Music Education (NAfME), general music curriculum should include singing, moving, listening, composing/improvising, performing, and reading/writing music. Playing musical instruments is a core element of this education. Students commonly have experience with percussion (hand drums, bells, shakers), woodwind (recorder), string (guitar or ukulele), and Orff instruments, but not brass.

Currently, brass is taught primarily in the context of band programs, which are widely accessible, but there are still significant hurdles for students wanting to learn brass:

1. The student must be attending a school with a band program and choose to join it (band is typically an elective course).
2. A student wanting to play brass is often pushed onto another instrument in the case that they aren't successful at the first attempt.
3. Students must have the resources to rent or buy an instrument in the case that the school cannot provide them.

Simply put, brass is a foundational pillar of the instrumental music world, and music and the arts are deemed a necessary part of a well-rounded education, yet brass is notably absent from general music.