^Not everyone wants to spend all that time at Universal though. And I have yet to see prices anywhere near that, we phoned up a year or two ago to see what an extra Universal day would be and were quoted over £100 per person.
Many people want a day in a park with a less insane crowd level and more relaxed atmoshpere. Spending so many days in Universal or Disney can become obnoxious, that's one reason why on holiday this year my family are only visiting the SeaWorld parks, not Universal or Disney.
You mustn't forget that SeaWorld also offers free parking with multi-day tickets, that would cost you an extra $20+ per day at Universal or Disney.