Because the survival of the tribe was at stake, and the strength of the Spirit of the Wilderness had a direct positive correlation with the tribe's power, they only worshipped their own Spirit of the Wilderness. In any case, the Barbarian Tribes were not interested in the gods of the mainland, even looking down on them with considerable disdain.
"So, what is your tribe's Spirit of the Wilderness?"
"Ours is the Ancestral Spirit, not some common mutt or stray cat."
Some Barbarian Tribes harbored hatred towards each other even deeper than their hatred for the Empire, and Boudica displayed a discriminatory attitude when speaking of this.
Lance hadn't even considered ancestor worship as an option; no wonder Boudica often shouted about the "Ancestral Spirit."
"Then, do you know of a tribe that worships the White Wolf as their Spirit of the Wilderness?"