Ever heard of Beethoven's Requiem? Schubert's 3rd piano concerto in b minor? Bartok's spectacular 4th symphony? No, neither have I.
Of course, all composers didn't write in all genres and forms. But why did some of them choose to skip important genres like the symphony and the concerto altogether?
In some cases, its understandable that a composer writes one work in a certain genre and then decides that it wasn't any fun, or that he wasn't that good at it. But in many cases, they didn't even try. The most peculiar example to me is, probably, the lack of Schubert concertos, considering his vast overall output.
So, what other neglected genres are there among the greater composers? And why?