Besides the great explanation
@BrianLo gave, it's also that the Disney Parks are wrapped up in everything that makes the Walt Disney Company the force that it is. Other parks can't have Mickey, Aladdin, Lion King, etc. Yes, they can make their own versions, but the style and character of the Disney interpretations of public domain stories are the definitive versions of these stories for at least a few more generations. Plus, to further
@BrianLo's point, just look at Hard Rock Park. There's not really room anymore for a brand new, large scale park on the regional level, let alone the national level, and the time it would take to establish ongoing marketshare while eating losses (or insignificant profits) is beyond the appetite of anyone fronting money these days. The economic reasons you cite aren't really applicable, at least in any kind of near to intermediate timeline, to the "reason" Disney is successful. Looking out another 10-20 years...because of COVID, I think it's possible you might see some kind of more tangible negative impact; otherwise I think
if there were any tangible economic impacts due to the reasons you gave, it would be more in the range of 30-40 years out.