It's a wedge issue.

The vast majority of people have no benefit from voting for right wing parties. Their policy seeks to benefit the very wealthy that support them. The want low taxes for the wealthy, all government services to be privatised so the wealthy can profit without risk and suppression of wages for workers.

The problem these parties face is only a very small minority of people would want these policies. So they need to create a reason to get people to vote for them.

They do this by inflaming and misrepresenting issues they don't really care about. But can be represented as a threat to the ordinary person. A threat they will be perceived to be the best to deal with.

Common wedge issues are racism, immigration, abortion, homophobia and now transgender rights.

Abortion has been a wedge issue in the US for a long time. There has been multiple opportunities for the right to completely ban abortion. They haven't because once they've done that they lose their wedge issue. However, they have been at it so long their is a generation of politicians that have been subject to this wedge issue so long they sincerely believe in it.

In the UK the Conservatives use alot of rhetoric about tackling immigration. However, immigration has risen in the UK under the conservatives. They also have plans to increase the number of visas from countries like India - which are much poorer and less culturally assimilated compared to people from the EU. This benefits employers as they can get cheap labour that can't realistically protest bad working conditions like UK citizens. Despite this people in the UK trust the Conservatives to tackle immigration better than the other parties.

Blatent homophobia or racism is now intolerable in main stream media. Even alluding to them is frowned upon. So these wedge issues aren't available to use anymore. But transgender issues are.