I think this is a huge part of it. It's the groupthink that is the downfall for everyone. Everyone has the same logic: "I want to wait to go to WDW until they open the new star wars land, but not before they open the flagship ride, and I should avoid going in December because that'll be super crowded because of winter breaks, so I should go in January/February which all the internet blogs say is cooler weather and low-crowd season." Except when everyone thinks that way, crowds are higher.
It's the flip side of how now, summer has been (comparatively) slow the last few years. Everyone is doing their "research" on the same blogs that say to avoid summer because it's hot and kids are out of school so it will be peak crowds. But our summer trips in the last few years have been far and away the least crowded because everyone thinks that way, and because even though kids are off school, they have three months in which to pick a week to go, unlike other holiday weeks throughout the year when everyone is off the exact same week.
The one thing that remains constant is spring break and christmas week are always crowd-city.