One of the comments on the article actually covered that the space shuttle was not qualified to shuttle crew to the ISS. It ran off of fuel cells that could not

One of the comments on the article actually covered that the space shuttle was not qualified to shuttle crew to the ISS. It ran off of fuel cells that could not be fully shut off. So the shuttle had a maximum mission length even if connected to the space station of 17 days. Whereas the soyuz capsule is qualified for 200 days. Which means that even if the shuttle took a crew member up, they had to have a spot on a soyuz capsule to get back.