Why should they be? If Disney pays below market wages, they'll continue to have staffing issues. If they continue to have staffing issues, their bottom line will suffer more than it would if they were to pony up an extra buck or two an hour.
Hell, let's do the math.
75k CM's - assuming they ALL get a $2/hr raise and they all work every day. That's an extra $150k in operating expenses daily. About $55 million per year.
The most recent numbers I've seen shown 12.7 million guests visiting WDW. That's an extra $4.50 in revenue needed per guest - not $4.50 per day: $4.50 total. Most guest will not feel that. A few cents here and there to adjust it is more than enough to get there without affecting Disney's bottom line. Hell, this could improve it given that a raise will likely cause more people to apply, helping out Disney's staffing shortage, and ultimately reducing overtime pay (which can be time and a half or double time), which will save Disney money.
But Disney doesn't look that far, or think that deeply.