They may have been less inquisitive but evidence shows they cooperated with each other on most things. They buried their dead, they hunted in groups, they took care of their ill and wounded members as evidenced in the many broken bones that showed signs of having healed found in their fossils.
They appeared to be less imaginative, a lot like some modern people who say "if it was good enough for Dad it is good enough for me!".
This would explain their lack of progress once they discovered how to work flint(which is a mystery in itself, if they didn't have much imagination how did they discover flint tools?).
Just to be very clear, I am not saying they weren't cooperative or altruistic or inquisitive at all. I am just hypothesizing that as a whole they were less of some or all of those (and probably other traits) than were humans as a whole.