One of the big challenged confronting the exploitation of space resources such as asteroids is a legal one. The international treaty that space faring powers are operating under prohibits countries, businesses and/or individuals from staking a claim of ownership over a celestial body.
It is expensive to launch a satellite or spacecraft. One of the biggest expenses is the one-time use of the engine and the fuel tanks.
It is expensive to launch a satellite. If there is a problem with a satellite, it would be better to be able to repair it in orbit than to send up another satellite to replace it.
Working in space is difficult and complicated.
The rocket engines currently in use for the exploration and exploitation of space are liquid fueled. Because they have to work in the vacuum of space, the fuel must be mixed with an oxidizer in order for combustion to occur. Elaborate systems have been developed to hold the different varieties of fuels and oxidizers in use. Complex systems of pipes and pumps deliver the fuel and oxidizer to the combustion chamber where they are mixed and burned.