For the Dallas area I think the lack of tornadoes was due to the cap breaking too late, mainly due to overcast conditions and from what I remember the 700 mb trough arrived a little later than modeled which also would've helped break the cap sooner. Looking at the 18Z FWD sounding the low level wind profile was almost linear in the lowest km which doesn't work so well for spin ups. There was also some subtle VBV above 1km but I don't think that alone was the reason we didn't see much, but moreso the combination of the two.