Actually, this post and the daily MU obsession on this board perfectly demonstrates why there is no SLU-MU series.
It's not complicated. Because SLU and MU are not rivals, there is room for folks like myself to root for both schools. I grew up in MQP country rooting for both school - we all did. Like many, I was forced to choose sides when the two played. Now that the teams don't play, emotionally it is very easy to root for both schools, and MU needs a strong fan base in Stl.
On the Tigerboard, SLU is never discussed - months go without a single mention of SLU. This is a good thing for Mizzou. At the moment, it is a one-sided debate - just a few immature SLU fans taking part. Prior to the couple of games the teams played, this sentiment was not terribly common, and it will eventually go away if the teams don't play. The bottom line is that it does not benefit MU to have a rivalry with SLU.
So, get over it. It's sad when there are only 2-3 threads a day on this board and at least one is about another team, in another conference, that your team doesn't play. Quite strange, really.