The developers saw the writing on the wall months earlier. There were no testing done by the developer or testers, but by the government. They were crammed into conference room with pizza and energy drink working past 10PM on a daily basis. Yep, that’s a recipe for a great product w/ little to no bugs.
To all the talking heads, 20 million visits is not 20 million unique user. For a system that supposed to be as big as ACA supposed to be, it supposed to be able to handle Pinterest level traffic with ease.