The RLE/RLT is a legacy from the old days (1970's) when a person requesting SRS was expected to disappear into the woodwork after surgery and it was meant to "get you feet wet" and "prove" to yourself and others that a woman's life was what you wanted and that you were capable of living a woman's life.
I suspect, as things changed, it was retained as a way to determine if you would truly be happy in whatever situation you would end up in after surgery.
With 'surgery on demand' in many countries now, I don't think it is as relevant - you pays your money and takes your chance.
It never was a "hard and fast rule" but a guideline. In the 1960's and early 70's I had lived nearly 10 years part time en femme (weekends and whenever I could get away from home) and when the opportunity for SRS came up, I had the full support of all my medical people.
The time en femme was very important to me and I learned a great deal. Being a teenager at the time, I learned makeup, fashion sense, and most importantly I learned a lot of the social skills that make 24/7 transition/SRS a snap. With that background, I slipped straight into stealth with nary a ripple.