.co is normally around 1/100 to 1/200 of .com so 1-1.co would be $xx to low $xxx to end user. It doesn't make sense paying around $25/yr for a name you hope to sell for low $xxx, hence the valuation of $0.
I do have few L-L.co names that I hold for nostalgic value probably, as I regged them at the very start when .co hopes were high and they are not any random ones either. But still not sure if they are really valuable. I mean ones like P-R, T-V, C-V