For space craft, the risk of development was considered to be massive and involving a lot of cutting edge technology. To offset the risk, a cost plus was used so the US government would bear a lot of development risk in exchange for owning all the technology.
The recent contacts were developed at a time when the US government felt that the technology to put people in space was cheap enough to go from cost plus to a fixed fee.
For space craft, the risk of development was considered to be massive and involving a lot of cutting edge technology. To offset the risk, a cost plus was used so the US government would bear a lot of development risk in exchange for owning all the technology.
The recent contacts were developed at a time when the US government felt that the technology to put people in space was cheap enough to go from cost plus to a fixed fee.