well if we take for granted that most new nicks are not real new players, but an old player who changed nick, the highest chance to get a realistic one is giving an average rating, so why not let them start from the middle, who goes up who goes down, most will stay.
Because the 'average rate' thing is strongly based on the fact that rate is correct, and if that is the starting point for all calculations...
And maybe if a nick is new its rating should move faster for x days, I don't know if you have that already implemented, I am just guessing
Etpro players change name every other day, and that keeps their rating low