I always thought the reason Brahms stands out among his contemporaries is that he's the first post-Beethoven symphonist who actually came close to Beethoven's level. But I've never been a big fan of the early Romantic era compositions.
Now, what process is used to teach a composition student to write music that, say, use techniques responsible for what happens in the first minute of the first movement of Schubert's B Minor Symphony, D. 759? It's one of the great beginnings to a symphony, but it isn't really written leveraging the techniques I described above. And while you can analyze it to figure out why it specifically comes off the way it does, there's no easy "divide-and-conquer" technique to abstract out and apply to other settings/styles.
That means there are fewer composers writing toy versions of moments like that to build up a deeper understanding of these other techniques. And there are many other musical techniques like this which do not lend themselves to pedagogy. Mozart is full of stuff like this, where the technique is essentially, "First, learn all the music. Next..." :)