Nobody knows what causes someone to be gender dysphoric. You might assume it is a mental illness or delusion. I fully understand why you would. But it is still an unproven assumption.
It was what doctors thought in the past and, you might be surprised to hear, most trans people seeking treatment or who got treatment years ago did too.
Surely is the first thing anyone would think of as it is obvious that reality is what it is so if you powerfully believe that reality is wrong with you then something maybe has gone awry.
They tended then only to assist medically those who approached doctors fully aware of reality and biology and the limitations of what could be done to merge perception of either but after thorough testing who still insisted that for some reason something was wrong.
Hormones or surgery was very much used as a last resort and - you might think paradoxically - only recommended if a person was considered mentally stable enough to understand the realities and consequences and cope with them.
This resulted in lots of analysing and testing and a search for causes that still goes on. There has been some recent sophisticated testing of gene groups and mapping of areas in the brain that are hinting at evidence there that might lead to finding a cause one day.
But we do not know right now and there might be psychological factors involved as yet untraced outside obvious personality disorders or other well diagnosed conditions which the gatekeeping before legal recognition is there to try to discern.
But not all trans people are the same in how they identify or see reality or labels or whether they want to change their body at all .
To get legal recognition today many find it hard to follow the rules so want to remove the barriers such as medical assessment preventing them.
That, of course, is the main problem for those outside looking in.
It is a question of balancing these two needs together somehow.
For me common sense is to be cautious and sure before taking such a major step in life. And seeing a doctor ought not to be an imposition but a sensible first step. But I am out of step in thinking that with a lot of people trans today who regard it as a choice.
It never was for me. Just a way to survive in the best way recommended by the many doctors I saw over several years.
To answer an earlier question I do not think the talk of 'de-medicalisation' would mean getting hormones or surgery without this. These checks and balances would remain for going that route.
But fewer would be seeking to physically transition if it made no difference to the ease of access to legal recognition (it is not necessary now but does make proving status harder and so rejection of recognition sometimes happens without it).
Plus they could probably access them abroad or off the net and by pass all UK checks.