We can send half a dozen robotic missions for the price of one carrying people. Just send two spacecraft for redundancy.
As to Hubble, that is pretty bad example. If people were present with Hubble they would be able to do exactly nothing. Everything was prepared on Earth and only then sent to space.
Also, the cost of servicing mission was almost as much as it would cost to make a copy of Hubble. The cost of servicing mission was reported 250M and the cost of sending Hubble was reported 4.7B but from what I remember most of this was R&D, making software, tools, developing plans, etc. A lot of spare parts for Hubble were already available (it is typical to have copy of everything on Earth for debugging and so on).
Robotic missions have the option of being scrapped and sent again which is not really an option for human missions.
As to Hubble, that is pretty bad example. If people were present with Hubble they would be able to do exactly nothing. Everything was prepared on Earth and only then sent to space.
Also, the cost of servicing mission was almost as much as it would cost to make a copy of Hubble. The cost of servicing mission was reported 250M and the cost of sending Hubble was reported 4.7B but from what I remember most of this was R&D, making software, tools, developing plans, etc. A lot of spare parts for Hubble were already available (it is typical to have copy of everything on Earth for debugging and so on).
Robotic missions have the option of being scrapped and sent again which is not really an option for human missions.