1) Some liberals simply view problems at home as more significant problems abroad. Help ourselves first, before we help others, ya know?
2) I used to consider myself a Wilsonian liberal in terms of foreign intervention - but I supported interventions in places like Rwanda, Darfur, etc., like places that actually need help. Iraq doesn't fit on that list, and that's why a lot of liberals were against the invasion in the first place.
So on the surface it might seem hypocritical and inconsistent, but there's logic behind it.