But they so rarely happen it's not worth the hassle. If you have the Tie option you can't trade the other outcomes without building up a big green or red on the Tie then you might be left with an uncomfortably large red that you have to redistribute just in case. It complicates the Cash Out feature as well.
The book is already 100% with three outcomes as the absence of a Tie option makes the Match Odds a Tie NO BET market.
You would be better off arguing for the Match Odds market to be Dead-Heated in the event of a tie, but I don't think short-odds backers would be keen.