Good point. We didn't see a major outbreak from WDW before shutdown. It's just not that clear cut to me.
The case numbers never made it up very high. What possible reasons? Weather playing a part? Still early enough in the timeline there to be saved from exponential explosion? People became a little more vigilant about washing and sanitizers? Maybe those reasons compounded each other and more?
Imagine more cases in the area than at the point of shutdown, and I'm packed into Haunted Mansion room, squished onto benches like Kilimanjaro Safari or FotLK for 20-30 minutes, or watching fireworks in a sea of packed people. Guests touching things and eating snacks without a second thought. WDW under normal operations is totally ripe conditions to foster spread. How could I really think otherwise? With enough hot people in there making few if any changes, I'd expect an exponential chain reaction and visitors bringing infection back to their low count communities.
There's a difference between no science and not enough data. Coronavirus has been with us for some time, just not all areas equally. Many places had the fortune of not having alot of cases prior to slow down. Don't forget, this thing grows exponentially. It takes a long time to build speed from 0 to 10mph. Once it gets cruising 30-90mph happens much quicker.