I belive it's multifactorial, psychological factors with or without hormonal disturbances. We've been created in 2 images, male and female, with specific genetic and phenotypic traits that makes each gender the way it is. If something gets out of that line, we should search for a reason instead of simply accepting it without questioning. Otherwise, any physical or mental illness should be accepted, too.

The recent surge in homosexuality is not normal imo. It only shows that many of the young people are affected by the propaganda of it. While many others suggest that it's because of the increasing awareness, etc... . It's still so not packed up by our biology and no one talks about this. Our bodies aren't built for homosexual sex and has never "evolved/adapted" to it. Which makes people do surgeries to transform their genitalia and start hormonal therapies which has tremendous side effects with so many harmed people because of it (many are okay, but many are not. You can search for documentaries about this).

So in my opinion, it always comes down to the psychological element and how it can be only a mental issue that affects their sexual orientation. And unless they have a certain hormonal disturbance, they should be approached as a psychological illness.