It almost seems like WDW is purposely making choices that benefit their smaller rivals. Universal and SeaWorld are probably grateful that they're going to have a month to operate out from under the Mouse's shadow. They'll be the main game in town for the locals for an entire month. That has to be very beneficial to them. And with Disney keeping their water parks shuttered, that helps the places that are opening their water parks be able to compete.
In order to phase into these reopenings, I would imagine one area of concern is flooding Orlando with tourists from all over the country and world. The way it stands now, with Universal and SeaWorld being opened first, then Disney opening a month later, it seems to me that they're targeting locals first and then expanding to the national and international guests. Not that national and international guests don't come to Universal and SeaWorld, but I think most of those also come for WDW, and if WDW remains closed, less national and international guests will come to Orlando just for Universal and SeaWorld.
I think there is a much bigger picture and a lot more in play here than "Disney only cares about money." I guarantee you SeaWorld and Universal care about money just as much as WDW, and are relishing in the opportunity they've got now to have an entire month in prime summer vacation time to welcome Floridians and others who choose to visit without WDW.