I don't understand why you need to ask this question.
The launching of the Hubble Space Telescope was so successful because it put the Hubble Space Telescope into orbit.
And the purpose of the launch was to put the Hubble Space Telescope into orbit.
Or perhaps you meant to ask a different question?
Maybe you meant "why was the Hubble Space Telescope so successful, and what was its purpose?".
Totally different question.
The Hubble Space Telescope was not the first orbiting telescope, but is one of the largest and most versatile. It is a vital research tool, but also an incredible public relations tool to bring the universe to the public. The images it has produced have captured the imagination of millions of people, and has helped to stimulate support and funding for space research.
Its purpose was to image objects more distant and in more detail than previous instruments - it could do this partly because it orbits above the bulk of the Earth's atmosphere and therefore doesn't have to deal with clouds, light pollution, smog, and daylight. It can devote hours or even days to gathering light from a distant object to make it clearer to study.
