So your only explination lies in a force unknown to science.
Since planets more or less are given equal pull in astrology we can deduce: The effect the planet has on us is not effected by a planet's mass. If it were then Jupiter would rule all and little Mercury would be left out. Also by astrologer's own claims distance isn't a factor as both Venus and Pluto have more or less the same measurable effect (in the sense that it effects us somehow).
So back to what I was talking about earlier, if distance and mass don't effect this force that rules our lives then what about the billions upon billions of asteriods in our solar system? What about the large transneptunian objects like Quoar, Sedna, Orcus, Eris, etc etc etc? And hey, distance isn't a factor, so what about the planets beyond our solar system? Scientists today accept exosolar planets are a pretty common thing, so fifty years ago why didn't some astrologer say "Hey, there are gaps in my data, there *must* be other planets out there."
By the rules of this 'unkown force' all the asteriods/planets/everything everywhere would simply be drowned out by the trillions of other celestial bodies.