What kind of visible-light and infrared telescopes on the ground are astronomers planning for the future? why are they building them on the ground and not in space?

Sharper images will be produced by the new telescopes.

Construction and maintenance is expensive

Explanation:

The telescopes are put in space so that unfiltered light is received by the telescope. Telescopes on Earth receive light after the light has passed through our atmosphere. This affects the final image of the telescope.

Some of the telescopes being planned in the future are the Extremely Large Telescope (ELT) with mirror aperture diameter of 39.3 m, Thirty Meter Telescope (TMT) with mirror aperture diameter of 30 m, Giant Magellan Telescope (GMT) with mirror aperture diameter of 24.5 m. These mirrors have a significantly larger mirror aperture diameter than the space telescopes. The ELT will be able to produce an image 16 times sharper than the Hubble Telescope. It is also very expensive to make an maintain a telescope in space.

Keeping all this in mind the new telescopes are being made on Earth.