I think Rupp does not want to attempt the world record as he wants to reduce the attention he is getting from the running community.
What would people say on Letsrun if he did break the indoor mile world record?
This says it all.
Official Galen Rupp twitter account. 26k followers. Last tweet 2012.
Official Mo Farah twitter account. 987k followers. Last tweet yesterday.
He shirley wants the record, but he doesn't want to blog.
Everything is focused on his running.
No time for twitter and increasing his fan base, which ironically would help him after he retires.