Your post makes me think you might be unaware of what happened leading up to 1973. The Faggots started threatening the members of the APA. They would call their homes and offices and threaten them. They showed up at the APA meetings as a mob, and threatened to hurt them if they didn't remove homosexuality from the list of mental disorders.
They conducted a multi-year intimidation campaign against the Doctors who were member of the APA, and many of them just didn't want to fight with a massive mob of potentially dangerous kooks. If you know anything about Homosexuals, you probably know that they tend to be particularly violent and vicious when their hate is aroused. Many if not most serial killers were homosexual.
They are truly sick, sick, people. The Doctors probably knew this better than any, and they knew what sort of people were threatening them. They knew these people didn't have normal impulse control, or rage control.
They caved. Scientific studies were irrelevant. What mattered was masses of wackjobs and threats.
I first got interested in the subject when I went through an MBA program in finance. I decided to avoid what I considered the touchy, feely courses in sales and marketing and instead took some 500 level courses in quantitative methods. There I encountered a psychology professor who was frustrated about the direction his concentration in abnormal psychology was moving. He was into the rigorous application of statistics for any doctoral committees on which he served, so he strongly opposed a recent decision of his association. I remember him as passionately opposed and unintimidated concerning the decision.