That's not exactly true though. Disney does have a unique non-duplicable product. If I go into my grocery store and see that a bottle of Heinz ketchup has gone up in price by $2, and I remember how it didn't taste as great last time, I can choose Hunts ketchup and get a similar experience for less and possibly a better taste.
I can't use my money to try the alternative Disney, I can only use it to go to Universal, which is a theme park, but if what interests my kids is Cinderella, Mickey, Moana, etc, then Universal isn't really a suitable replacement and is like switching to mustard instead of buying ketchup.
Same can be said in reverse: If myself and/or my family was into Harry Potter, I don't think they'd be happy if I said we were going to WDW instead of Universal because the quality in relation to cost has gone down.