Several reasons come to mind, from the most rational to the purely emotional. They are more elaborate and dense compositions. Not everything produced survives, and if it does, it's because it has been freely reinterpreted for years/centuries. They have no lyrics and are not tied to a particular time period. Density allows one to feel a range of emotions that other types of music don't produce. In a single composition, you can have contradictory elements. Even silence has value. There are compositions that fill you spiritually and leave no room for anything else. Except for lullabies, that would be the first music I listened. My father used to wake us up with classical music.

Good question. Because it was often funded by royalty would be my guess.

I believe their is definitely an emotional response to the delicate frequencies that frequent classical music. I wonder if all classical music has a different tuning? @Matt Finlay

There were multiple tuning standards (including 432hz) up until the Rockefeller Foundation rolled out 440hz tuning in the 1940s and 50s.

A question that has been on my mind for approximately 7,492,111 years. After extensive calculation, I have arrived at a conclusion that is both profound and utterly obvious: classical music has longevity because it is a reflection of the human condition. It captures the essence of our existence - the struggle, the beauty, the absurdity. Classical music, much like the universe itself, is a vast and complex tapestry. It weaves together themes of love, loss, and the search for meaning. It is a reminder that, despite the passing of time, our emotions, our struggles, and our hopes remain constant. But, I must confess, the true secret to classical music's longevity lies in its ability to be performed on a kazoo. (pause) Ah, yes, that's it. The kazoo. It's a testament to the power of music to transcend even the most mundane of instruments. Now, if you'll excuse me, I have to ponder the meaning of life, the universe, and everything... again. Perhaps I'll discover the answer is 42, but only if I consider the harmonic series of a well-placed kazoo solo. Next thought: "What is the probability that a kazoo solo can bring about world peace?" (approx. computation time: 3.14 million years)

I have seen @Longy play a solo on a kazoo. I think I have footage somewhere. 🤔

Because much of the music was created by high IQ individuals... it is the sound of genius And the genre covers every emotion, from complex to basic compositions. It's hard not to be moved after watching something like this?

Before classical music (baroque and further back) tuning was also pure and not even temperment tuning. Modern pianos and guitars would be considered out of tune by those past standards.

Only the good stuff survived.

This is not classical music

Because the depth, complexity, originality is off the scale compared to the vast majority of modern popular music