I think it might be a little of both. Found my first one, a single egg, here in a suburb of Pittsburgh way back on June 4th, then practically nothing for over a month. They have started to become somewhat more common in the past two weeks, but are still not as prevalent as in past years. Milkweed quantity and quality seems to be less than normal as well. Perhaps it grows in cycles somehow, or is just responding to our climate changes or something.