I suspect it has more to do with the fact that when we post we want someone new, who may niether have the time or inclination to go back reading through a lot of historical posts, to know where we are coming from.
I like my answers to be correctly understood in context, not missunderstood becuase the reader, whom I've often not seen before, doesn't know who I am, what I've done in life, and where I'm coming from.
And now here (in the italics) is a very tiny but entirely relevant example:
One feature which I miss on Susans, which exists on two other non trans forums which I moderate, is the ability to write a biographical paragraph or more in my profile. If we had that then I for one would not feel the need to do this.