I don't know why but they did. On every E-store they make no mention of SLI and if you look at these close up's there is no SLI "finger" on the PCB.
These are all different models from different partners but they are all GTX 650 Ti's and as you can see there is no finger for SLI.
This is a close up of the 650, again no extension for SLI.
However if you look at the 660 and 660 Ti they are listed as SLI ready.