They are not "selling vacations at a loss".

For goodness sake ... welcome to the world of business.
Why do you think businesses sell stock? They do it to bring in money so that they have some operating funds. If not, then consumers would have to provide 100% of the cost of something, and none of us would be able to afford anything.
Let's make believe that one person's WDW ticket was equal to the daily pay of one WDW CM. (It's not, but for sake of example, let's go with that.) There are 55,000 CMs at WDW. So the first 55,000 people through the gate on any given day are doing nothing more than paying the salaries of the CMs. If you look at an average of 120,000 guest per day (WDW's annual estimated attendance of 47,000,000 divided by 365), that means that just under half of the money coming in every single day goes to simply paying cast their hourly pay rate. Doesn't include benefits or costuming or any other CM costs. And, really ... a good percentage of the people walking in the gate every day are using APs or comp tickets or the 10th day on a 10-day pass, which costs about $3, so it's not really equitable, but let's imagine that it is.
So ... you've paid the cast and you have 65% of your gate income left. That has to cover everything else -- ride and show development, maintenance, utilities, transportation, lighting, audio, safety, costumes, parade floats, attraction parts, equipment, decorations, water, fireworks, etc. Obviously, what's coming in the gate is not covering 100% of what it takes to offer the Guest the vacation they get when they walk through the gate.
The company says, "Gee ... how are we going to cover the rest of that cost?" They could double the cost of tickets, but that's not likely to go over well. So they find sponsors for things they can find sponsors for, and they get the rest of the money by issuing stock. People like me purchase stock and provide Disney with an influx of cash to continue building and operating the parks. Then, if Disney has done their job properly and used my money well, in a few years when I need some funds, I sell that stock for more money than I paid for it, thereby netting myself a profit. Somebody else buys the stock I just sold, thereby sending more money into Disney to use as above. Lather / rinse / repeat.
Basically, I've loaned WDW $21 per share of the stock that I've purchased, and when I sell it later for $34 a share, I make a little money for having done that. Not exactly a pyramid scheme.
Welcome to capitalism and the stock market.