The Hubble space telescope is in the space instead of on the ground because if it would've been kept on the ground, the interference of the atmosphere would have disturbed its operation.
Explanation:
The atmosphere that envelopes the Earth is known to absorb lights of certain wavelengths. Thus, to avoid the distortion caused by the interference of the atmosphere, NASA has preferred to place the telescope in the space instead of on Earth.
Moreover, it would've also been impossible for the telescope to focus on a single entity there for more than 12 hours if it would've been placed on Earth.