When, in 2018, Theresa May first mooted this legislation, her government said it wanted to end 'abhorrent conversion practices' including 'gay cures'. These ranged from 'pseudo-psychological treatments' to surgery and even 'corrective rape'.
Yeah, OP, I mean, corrective rape is obviously already totally illegal.
It's illegal to force people into therapy.
Psychotherapists have a professional body with standards (that don't allow for anything like "conversion therapy") and can lose their licence to practice for that kind of thing.
At the same time, sexuality is complex. People can have all kinds of experiences and problems related to what they see as current problems in their sexual life. Scientifically, we don't even know that sexual preference is set in stone, or what forms it, or whether it is the same set of things for everyone. And adults are entitled to their beliefs, especially about their own experiences.
The law isn't really the place to be defining that. Non-consensual and abusive treatments are already completely illegal.