Part of the issue is related to breakdowns of logistics and resupply, since often roads are either damaged or flooded.
If there's problems getting fuel or food into the area that means what's already there needs to be adequate until resupply at the normal rate is able to occur again.
The local gas stations can only store so much fuel on site, for example. If they're in a high volume area they're not going to invest in substantially higher on site storage capacity, they're doing to arrange more regular deliveries.
Same goes for all sorts of other goods. Walmart doesn't build the back storeroom 10x bigger because the store has especially high traffic, they just schedule more deliveries and put more of the most in demand goods on each delivery.
If they normally sell 40 widgets a day and keep 120 in stock, but now resupply of widgets is likely to be interrupted for the next 4 days, some folks are gonna have to do without widgets for a day. If tourists make up a quarter of that demand, having no tourists for those 4 days would mean the existing widget supply won't be exhausted before the next anticipated delivery.
Further, if keeping ~120 widgets in stock is the best balance between supply and storage requirements, why would Walmart store more of them on-site unless they're forced to? Maintaining a higher than ideal supply just costs them money, either because it's eating into storage space for some other goods (impacting the ability to optimize in stock storage of those goods) or because they had to build a larger facility than ideal which adds to their overhead.
Much of the resource planning is motivated by profit margins, there's no incentive to use local (privately owned) businesses as warehouses in the event of emergencies, so why would you blame the people who do the planning in that context for not doing something that's literally both not their job and counterproductive to what their job actually incentivizes?
The tourists get blamed because they don't need to be there, they chose to be there.
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