why were people in the early U.S. space program disappointed by their failure to launch rockets before other countries?(October Sky)

Because this failure put the United States in a position inferior to the USSR, in terms of technology.

Explanation:

The space race took place during the cold war, where the USA and the USSR competed with each other, to establish greater admiration and influence among other countries. In this case, it was important for the USA to be more modern and technological, launching a satellite before URSSA, which did not happen. This was seen as a failure, which allowed the United States to appear inferior to the USSR.

To show off the "Great White Fleet" and impress other countries around the world with U.S. naval power, to allow the Navy to gain the experience of worldwide travel, and to drum up domestic support for his naval program.