Space telescopes offer advantages for particular types of observations, but there are many types of observations for which ground-based telescopes are superior. The basic advantages that ground-based telescopes have are:

* Larger collecting area, which means more photons collected, which means you can see fainter objects.

* With adaptive optics, ground-based telescopes can actually achieve better resolution than space telescopes over small fields of view.

* Ground-based telescopes are far easier to maintain and upgrade.

* Much looser weight, size, radiation-hardening requirements mean that you can do things on the ground that would just be unthinkable in space. You can attach things like massive spectrometers to ground-based telescopes, without having to worry nearly as much about form factor and weight, or whether radiation will damage your electronics.

The advantages that space telescopes have are:

* No weather to deal with.

* You can observe UV and IR wavelengths which the Earth's atmosphere absorbs or emits in - which is extremely difficult/impossible from the ground.

* You can get high resolution over large fields of view. However, you can't reach the same resolution on small fields of view, because ground-based telescopes with a large aperture + adaptive optics will beat you there.

Basically, at any fixed budget, you will be able to build a much larger, more complex instrument on the ground. You only go to space when there's a compelling technical reason to do so (e.g., you need to observe UV light).