Because of the expense, the level of dangerousness and because the cold war had already ended.
Explanation:
With the end of the cold war, the space race was no longer so important that there was no reason to maintain a dispute with Russia. In addition, space exploration was a very high investment for the government, which preferred to invest in things that are more popular and accessible to everyone, such as commercial travel. This economic issue, added to the danger that space explorations posed, meant that the government had no interest in supporting international travel.
