Wow today is packed, it seems Mondays aren't the best weekdays to visit?

I'm new to having a pass and trying to figure out the best times and days to go during the week with my son since I'm a SAHM. For some reason I thought today would be uncrowded but it's the most packed it's been since we got passes! Is there any rhyme or reason to crowds? I know the holidays are typically just busy regardless because of the decor and characters etc but would love some insight!