I can't fault your logic, but putting parks on hiatus for revamp/refurb/construction doesn't seem feasible. For example, if they closed Animal Kingdom to fix Expedition Everest, gut Dinoland USA and retheme, and possibly add a ride to Pandora, they would have to displace staffing for that entire time period (you could theoretically use them to staff said 5th gate but then you're severely short staffed once AK comes back online, not to mention Central Florida / metropolitan Orlando is already suffering an amusement park staffing shortage), they would still have the maintenance expenses for all of the the live animals without having park admissions dedicated to offsetting that park's expenses (a 5th gate would only cover expenses within its walls, not those of shuttered parks), and even if you were to close every Disney park in FL each for a year for upkeep, refurb, retrofit, and expansion just to justify the expense of building this 5th gate, you have a full 5th park at the end of that five year window with four other fully functional, expanded capacity parks also online. What do you with it?