In the bad old days we stored data on spinning-rust harddrives. In order to find the data you wanted you had to position the reader head. This took several milliseconds. You could read a lot of data in that time. So basically if you took the trouble to seek somewhere you better read a bunch of data to make it worthwhile.

People would even run defragmenters, that would rearrange file blocks so they were stored continously and the whole file could be read without seeeking.