Why did Reagan end commercial satellite launches from the s.shuttles?

In this lull before the CAIB Report, and in the midst of the sad news
about M. Speegle (my grandma's funeral mass was last weekend,
co-incidentally), I decided to post this old-news question. I've
always assumed that the govt was afraid it could be sued if a shuttle
failed with a pricey comm. satellite on board, but I've never been
sure about this because couldn't they just write up a biz contract
forbidding a lawsuit? This really put a dent in the true, logical
usefulness of the space shuttles, plus a way for the govt program to
make money. Who convinced Reagan to sign this? Anyone know the whole
story, or any interesting pieces of it?