Most the parks don't have enough cash on hand to do this for long. Without revenue, the parks will become insolvent at some point and tax breaks don't help on that side of the cash flow. If this is a 3-6 month issue, solvency becomes a real issue.
Looking at the limited reopening of Shanghai Disney isn't promising for what is even feasible for a park to do in this pandemic. That limited opening can't be bringing much revenue in and isn't sustainable.
You are exactly right. And the reality is, the amusement industry is pretty much considered a luxury item in the scheme of life. If we see a breakdown of large scale proportions, no one is going to be thinking about how to save SEAS or SIX. We might be wondering how to save Safeway and Food Lion.