Cavemum, that's because the 90% are not transsexual - the only ones who are covered by the Gender Recognition Act right now. They are transgender and have no medical condition and so do not want to alter their bodies or see doctors.
This is why there is such a fuss right now to alter the act, remove the necessity for dysphoria, not require any medical assessment or treatment and just self declare that you have changed sex. And be allowed to do so.
It is quite obviously absurd and no sane government should be even considering it.
Of the just under 5000 transsexuals who have been recognised in the past 14 years just over 3000 are transsexual women and the others are transsexual men.
Surgery is more uncommon with transsexual men as options are limited and more recent. Some transsexual women do not have reassignment surgery due to age or ill health but the majority do as that is what dysphoria means as someone posted earlier.
There are no exact figures but it is believed that about 60% of the transsexual women in the 3000 covered so far have had surgery. And the others have all been psychiatrically assessed. Copy birth certificates can only be altered with support from two doctors.
If self D is introduced all of that will be meaningless as the majority of those by passing doctors altogether and gaining legal status will have a penis.
Therein lies the problem.