A few potential answers:

• Many times, ideal situations will be fairly close to the “real” answer, at least within an acceptable margin.
• You have to learn about the physics in the most basic sense before you can start adding on more complex physics and math. Many topics are just extensions of simpler problems with some added nuance.
• The more complex problems may require an understanding of the interactions at an atomic level, and it’s just not relevant to enough people to teach it in general classes.
• The math on more complex interactions often require more complex math than what you have learned at your given stage in school.
• The math on more complex interactions may also be “unsolvable” in the sense that you must use brute force iterative calculations to come to an acceptable margin of error.