I refer you to U.S. Code: Title 10 Subtitle A Part II Chapter 37 § 654
Policy concerning homosexuality in the armed forces
(2) There is no constitutional right to serve in the armed forces.
(3) ... it lies within the discretion of the Congress to establish qualifications for and conditions of service in the armed forces.
(8) Military life is fundamentally different from civilian life in that ... the military society is characterized by its own laws, rules, customs, and traditions, including numerous restrictions on personal behavior, that would not be acceptable in civilian society.
(12) The worldwide deployment of United States military forces, the international responsibilities of the United States, and the potential for involvement of the armed forces in actual combat routinely make it necessary for members of the armed forces involuntarily to accept living conditions and working conditions that are often spartan, primitive, and characterized by forced intimacy with little or no privacy.
(13) The prohibition against homosexual conduct is a longstanding element of military law that continues to be necessary in the unique circumstances of military service.
(14) The armed forces must maintain personnel policies that exclude persons whose presence in the armed forces would create an unacceptable risk to the armed forces’ high standards of morale, good order and discipline, and unit cohesion that are the essence of military capability.
And the pièce de résistance:
(15) The presence in the armed forces of persons who demonstrate a propensity or intent to engage in homosexual acts would create an unacceptable risk to the high standards of morale, good order and discipline, and unit cohesion that are the essence of military capability.
The entire policy can be found here. And it is well worth reading.
So exactly what about homosexuality has changed since 1993? Do openly gay soldiers all of a sudden not damage "morale, good order and discipline, and unit cohesion?