I believe the purpose was to bring material to LW from outside rather than quoting each other (and especially, quoting Eliezer), to avoid an echo chamber effect. There was once an experimental LW Quotes Thread, but the experiment has not been repeated.

I don't have a strong view about whether LW regulars posting on other LW regulars' blogs should be excluded from the quotes threads, but I incline against the practice. It was a good quote though.