It's a cost model, they probably have a coefficient for what % of people they think will wait vs. go elsewhere while the website is down. When you're running a retail company, you have to at least attempt to quantify lost sales in order to model your business.

There's no way to measure lost sales with high accuracy, but that's not really the point, because it's most useful for modeling decisions and policies in a forward-looking context. Future revenue forecasts, the other term in the equation you're optimizing, are also inaccurate.

These functions are also generally "bathtub" shaped, and with the amount of money at stake, you can save quite a lot by being a little closer to the optimum, so they're worthwhile.

Yeah some people determined like me probably tried over and over until it succeeded, it was a bit scary clicking refresh during the actual payment (although was monitoring my credit card charges, was prepared to cancel extra orders and at worst return extra stuff) , fortunately it went only once despite multiple refreshes until I saw the confirmation page.

Other people probably just went directly to stores.