I assume there are several reasons for this.
* Confusion, sown by schools.
* A false depiction of the Fabulous! gay lifestyle, sown by Hollywood.
* Whites are so demonized, some seek to escape their "oppressor" status by identifying as an "oppressed minority."
In the pre-Stonewall days when these behaviors were suppressed, research showed that while as many as 4% "identified" as LGBT in late teens through their 20s, the percentage who stayed that way steadily decreased in the 30 and above age groups. Sufferers either realized we're not made to be that way; improved their self-esteem in the workplace, resolved whatever childhood or adolescent dilemma pushed them in that direction, rejected the many "yuck" factors of the actual gay lifestyle, etc.
I'd still like to see a reputable study of the numbers of people "identifying" as LGBT who were sexually abused as children. Research into any cause except "born that way" has been shut down and the proponents of it vilified.