Good to see you back. Try not to get yourself banned again
I think they do it in an attempt to make people care about Smackdown more. It's not very realistic, since Raw usually has the big names, and considerably more of them - lets take a look:
They're even at this stage, but Raw clearly has the bigger names. But they try to make it look realistic when it's SD vs Raw on PPV, by having the Raw team fall apart somehow. It's been done to death and they ought to change it up this year!