I personally know clinicians who have declined to take on work for the court because they are well aware that if they say anything that can even be remotely construed as not completely supported of "affirmative care" they will be personally harassed. As the contributors say, it is not worth it.
I would add that this is not just a fear of being harassed by anonymous social media trolls. This is fear of being harassed by other clinicians with activist agendas. Those protesting the CAN-SG conference - both online, and in person - included many clinicians...
The Cass review, if anything, may make this worse. The review makes it clear that the evidence base is poor, to say the least. So a clinician is unlikely to testify that these treatments are, in general, a good idea. But then they are too afraid of the consequences of telling the truth...
ETA if judges exercise discretion to allow clinicians to give expert evidence anonymously, I suspect that there will be (1) many more people willing to accept the court's instructions, and (2) those people will be far more candid.