It is not clear that there is much to be gained from measuring short term human exposure to space flight any more with all the data that has been amassed to date.
Shuttle flights are more dangerous than straight multistage style flights since there aren't any tiles.
We have had drone technology since at least 1944-- automated B17s (Aphrodite) overstuffed with explosives, piloted by remote control.
We might consider automating the shuttles and tool up for USA-Soyuzes or Apollos again. (I have heard that there are practicality issues with recovering Apollo technology, skills and mfg capability?)
I guess in the past that relying on Russian vehicles exclusively for human space transportation would have been politically unattractive and would have posed difficult cross-organizational and cross-cultural management issues.
Losing an unmanned shuttle would have been a lot easier to take than losing a manned shuttle.
Ripping out life support systems from shuttles would save weight and permit larger equipment/fuel payloads.
If this idea was considered and rejected in the past, it might still be worth re-considering in the present circumstances (with new environmental restrictions, the fall of the iron curtain, etc.).
Because there is something about Humans that makes them want to go. If Humanity ever loses that basic instinct then space exploration will die.