Because I have just been reading his Pagan Religions of the British Isles. There were'nt that many "venus" goddesses found in Europe and it really depends on interpretation of what was found - only a small number over a large area, could have been more to do with fecundity.
I know we have Sulis in Bath, plus the "three matres" (probably to do with roman soldiers missing their mothers ;) .. He blames a lot on feminist writers for too much emphasis on the female role. I know there is a certain controversy about it, but I think there were gods and goddesses playing equal but different roles, it can't be otherwise, but I'm sure someone will say different.