This is an old post by Adams, but I want to highlight it because he makes an apt observation about the nature of many new composers’ pieces:
But back to the typical instrumental composition: The slow, nervous, unsettling introduction will most likely be followed an up-tempo OSTINATO. The ostinato has gained great prestige of late because students wrongly believe that this is what made Steve Reich and Phil Glass successful composers.
His explanations for why ostinato is such a prevalent technique only get about half the job done, however. Here they are:
[Student composers] misunderstand the essence of minimalist technique, thinking that by merely introducing a repeated, grinding rhythmic figure they can achieve satisfying musical form.
Unfortunately most young composers come to their profession with little awareness and even less interest in creating a unique harmonic profile for their music. This is one reason why so many pieces resort to OSTINATO—it’s a kind of default mode to create a gravitational sense in the music.
I’d say both of these are accurate. But it seems to me the primary reason for the abuse of ostinato is that it’s easy. If you don’t really have an idea of where your piece is going, either specifically (in the foreground), or in a more general, background sense, it can be extremely arduous to produce even one measure. And then, you’re not even guaranteed that the measures you manage to string together will work or cohere. An ostinato is like “instant content,” or “instant length.”