Here's an article on CBC (equivalent to BBC in Canada) showing one reason why self-ID (or light touch and poorly executed medical gatekeeping) might be misused and how easy a sex change has become in a country that fully embraces 'you are who you say you are'.
www.cbc.ca/news/canada/calgary/change-gender-identification-insurance-alberta-1.4754416
The guy in the article 'changed sex' to save money on car insurance. Not an issue in the UK because sex discrimination when it comes to car insurance was ruled illegal by the EU but shows that for some people at least the desire to save money / stick it to the man is enough of an incentive to make what is supposed to be a fundamental change. Making changing your birth certificate, driving licence etc an easy piece of admin means people will do it for all sorts of reasons, most of which have nothing to do with gender dysphoria.