Sponsors offer sweeps in lieu of regular advertising, so promos wax and wane throughout the year with Christmas *usually* the hottest time for IW/DP types of promos
I've also noticed the amount of sweeps with prizes I'd like to win waxes and wanes so it seems like there are less than usual - seems sponsors offer the same type of GP {ie Trips} around the same time frame & especially during Football season.
I also haven't found as many IW's to list as I did in past years either, and figured it was a function of the economy - when the crash {2007/2008} happened, I expected sponsors to drastically pull back on sweeps, but they barely did at that time.
Now, with economy [finally] roaring back I think sponsors are focusing their ad $$$ on more TEXT to WIN & switching from entry forms/logins to blogs/facebook/twitter entry so that it makes the total prizes/promos to enter for seem even smaller if you prefer to skip those entry platforms.