On a basic 7 day vacation it costs a family $21 so most people will say no big deal. I don't know how many cars pay to park per day at Disney but IF we assume it's 5,000 cars per day just to look at some numbers - that would come to 5.5 Million Dollars annually.
After taking a quick look at the google maps satellite view taken on what appears to be a typical day (based on which lots are full), I'd estimate it's more like 10,000 cars per day. That would bring in $73 million per year all told, which is obviously far above the cost of operating and maintaining the parking lots.
But over 5-10 years this is getting into the ballpark of the costs of the new roads, bridges and parking lots in the MK and TTC area, plus the new garages for Disney Springs and DHS.
An extra $21 per week may not sound like much and it may be hard to imagine any family saying, "That's it, I quit this vacation!" But the law of supply and demand is just that, a law. People are sensitive to prices, and everyone who's ever bought or sold anything knows that. People are so sensitive to the appearance of prices that many businesses take the trouble to give things prices ending 999.99, to avoid the sticker shock of high, round numbers.
Besides the sticker shock at seeing a $20 charge on the parking, there's the question of the perception of fairness. MK's parking lot changes are apparently due to Disney's desire to build at least one and possibly more condo towers around the Lagoon. For a great, big profit. Should offsite Magic Kingdom guests subsidize that? Disney Springs is a glorified shopping plaza with tenants and everything. Are the retail receipts expected to be so sparse that guests visiting elsewhere on WDW property have to pay for the parking arrangements? And the DHS parking garage is ultimately just a big screw-up born of bad park planning and bad management of the park's evolution of layout and attractions. How is that the customer's fault? Because they have the bad luck or bad taste of being huge Star Wars or Toy Story fans? At least, the approx. 15% of them who visit DHS on any given day. The parking fees may also be subsidizing the monorail and bus system, which again seems like making one guest pay for someone else's freight. Aren't Disney hotels and especially monorail resorts already very expensive? Add to that the perception that $20 is far too much for the cost of operating a parking lot, even with a healthy profit, and that an 18% increase for the price of a simple commodity purchased from an already hugely profitable company is just not right.
It's not a big deal ... but it says a lot about the company's mindset right now. You can consider these complaints to be the equivalent of a very large eyebrow being raised ... like ... $20 per day ... really? And it's OK because the price increase adds up to the cost of a large lemonade every day, and because Universal will do the same thing a month later?