I think there are several reasons. First, the abstraction of a stream of data is useful when a program does more than process a single realtime loop. For example, adding a timeout to a stream of data, switching from one stream processor to another, splitting a stream into two streams or joining two streams into one, and generally all of the patterns that one finds in the Observable pattern, in unix pipes, and more generally event based systems, are modelled better in push and pull based streams than they are in a real time tight loop. Second, for the same reason that looping through an array using map or forEach methods is often favored over a for loop and for loops are often favored over while loops and while loops are favored over goto statements. Which is that it reduces the amount of human managed control flow bookkeeping, which is precisely where humans tend to introduce logic errors. And lastly, because it almost always takes less human effort to write and maintain stream processing code than it does to write and maintain a real time loop against a buffer.

Hopefully this helps! :D