There isn't a great deal of pressure from TRA to change much about the GRA. The advantages of a GRC are a new birth certificate, to be recognised by HMRC, be married in the aquired gender, not actual sex, and maybe prisons now, but who knows.
If none of that is priority, why bother committing to a GRC and having an official record of your transition?
The reason why activists pushed for GRA reform is to advertise the process and normalise the idea that men have to have female id and be in womens spaces to facilitate getting a GRC. And the idea that businesses, workplaces and the public cannot stand in the way of the legal process.
The process has always been self id because the diagnosis and the paper work are very easy to get. The only issue is time, and labours proposal didnt really address that.