They aren't paying all of the cost. We've been down this road before. All of the expenses are audited by an independent public accounting firm. There's no way that a large number of people are colluding to help charge more to DVC owners. There would be no incentive either for those individuals. Also remember that DVC is a separate division from the hotels. Why would an accountant or even senior management at DVC care to make the hotels more profitable. They aren't getting credit for that.
Tin foil hats and conspiracy theory aside, they do share the costs of common amenities like transportation, parking lots, pools and in some cases Bell Services. I'm assuming the allocation is based on the number of rooms each side uses in a given year. Since DVC is 95%+ full they take a nice chunk of the common costs, probably not over 50% but still a decent amount of money. Let's take BLT for an example. Owners will pay $1.8M for transportation for 2017. That covers a portion of the monorail, buses and boat. They didn't add extra buses or monorails when BLT was built and there is no dedicated DVC transportation so the CR has reduced their overall costs by $1.8M by having DVC owners pay for a portion of the transportation expenses. That's pure profit for CR. This also applies to things like real estate taxes, security, certain maintenance items related to shared common areas, etc...It allows the hotels to increase profits by shifting some of the fixed costs to the DVC side.