I know a few "Disney adults", and when they have a trip booked, they are absolutely buzzing in the lead up, and plan their trip to a T. They feel the magic and love going.
Same here. They are actually very smart and talented people in real life so it's hard to dismiss it as an educational or class thing.
I feel the closest thing you can compare it to is a religion. The entire Disney universe clearly has a spiritual element for many people. It invokes a good feeling, a sense of community, shared imagery and stories and the ability to escape life and believe in a "magic" that's bigger than yourself. And of course, in an age where more people aren't actively religious, pop culture and fandoms take over to fill the same need for believing in something.
And of course, for outsiders, some religions and the behaviours associated with it are just bonkers. However socially, you still need to respect religious beliefs even if you cannot relate to or empathise with it in any way on a personal level.
It's also interesting that virtually everyone gets introduced to Disney at a very young age, just like most forms of religion. It's easier to indoctrinate a mind that is easily impressionable than to force older people into accepting something new. Loads of adults forever associate Disney with the nostalgia and happiness of childhood. The same feeling you have when remembering how Christmas felt like when you were small.
A trip to Disneyland feels like a pilgrimage for many fans. The ones I know have a yearly pass and actually go back at least 4x a year so they get their money's worth. They're also buzzing beforehand in a way you can only compare to a spiritual excitement. It's not just mundane excitement over a city break or beach hol. The crowds, heat and long waits don't really matter in that context, just like people going to Mecca or Lourdes genuinely don't care about how many others are also there.